In an age of overflowing inboxes and unforgiving spam filters, email deliverability has become the make-or-break factor for marketing success. After all, “it doesn’t matter how good your creatives or offers are if they never get to the email inbox".
What Is Email Deliverability and Why It Matters in 2025
Email deliverability is the ability to get your email into subscribers’ inboxes (not bounced, not filtered to spam). It’s essentially your Inbox Placement Rate – the percentage of sent emails that actually land where your recipients will see them. This is the critical foundation of email marketing: even the most brilliantly crafted campaign is worthless if it’s stuck in spam. Deliverability isn’t the flashiest topic, but it is arguably the most important part of email marketing.
Why is deliverability such a challenge in 2025? For one, mailbox providers (like Gmail, Outlook, Yahoo, etc.) have gotten much stricter. Spam is still a gigantic problem – roughly 347 billion emails are sent each day and over half “are estimated to be spam,” according to industry research. Providers are constantly raising defences to protect users from this “mayhem.” In the last year or so, Gmail and Yahoo even introduced new requirements for bulk senders that effectively force marketers to follow best practices. Meanwhile, privacy changes (like Apple’s Mail Privacy Protection and new inbox features) mean traditional metrics and tactics are shifting. Reaching the inbox is getting tougher, and marketers must elevate their game to keep up.
The stakes are high. Undelivered emails aren't just lost opportunities—they represent a significant hidden cost for UK businesses. According to the DMA's 2023 Email Benchmarking Report, a 1% drop in deliverability can result in a £700 revenue loss per million emails sent. Considering that approximately 10% of permission-based UK marketing emails end up in spam folders, businesses could be facing losses of up to £7,000 per million emails due to poor deliverability. Data Marketing Association
Beyond direct financial implications, there's the issue of customer trust. While consumers might not explicitly mention "deliverability" issues, they do notice when they don't receive expected emails. This can lead to frustration, diminished trust in the brand, or even unsubscribes. Moreover, managing unwanted emails and spam can be costly. A study highlighted that managing unwanted emails could cost UK businesses over £34,000 annually, factoring in employee time and IT support. hrreview.co.uk
In summary, ensuring high email deliverability is crucial not only for maximizing revenue but also for maintaining customer trust and reducing operational costs.
The bottom line? In 2025, email deliverability is mission-critical. It’s the difference between your message being heard or being invisible. The good news is that improving deliverability is very achievable – and often means simply doing email marketing the right way. Let’s break down the key factors that determine whether your emails hit the inbox or hit a wall, and how you can tilt the odds in your favor.
Key Factors That Influence Deliverability
Achieving great deliverability isn’t luck; it comes from nailing a few technical and strategic fundamentals. Here are the key factors that influence whether your emails land in the inbox or get filtered out:
Authentication Protocols (SPF, DKIM, DMARC):
Email authentication is step one for modern deliverability. Think of it as proving to mailbox providers that you are who you say you are. Major inbox providers now require bulk senders to authenticate emails via SPF, DKIM and (ideally) DMARC. SPF (Sender Policy Framework) is essentially a DNS record that says “these mail servers are allowed to send on behalf of my domain” – it helps prevent spammers from spoofing your address. DKIM adds a digital signature to each email, which the receiving server checks to ensure the message wasn’t altered and truly came from an authorized domain. DMARC builds on SPF/DKIM by telling providers what to do if an email fails those checks (e.g. reject or quarantine it) and by providing reports on email authentication results. Together, these protocols vouch for your identity. Without them, your emails will almost certainly get suspicious treatment or outright blocked by Gmail, Yahoo, and others. If terms like SPF or DKIM sound intimidating, don’t worry – most email service providers (ESPs) have guides to set them up, and once configured, they run in the background. The key is not to skip this; authentication is now basically a ticket to play in the inbox.
Sender Reputation (IP and Domain):
Your sender reputation is like a credit score with mailbox providers. It’s a measure of how much they trust your sending IP address and domain based on your past sending behaviour. If you consistently send emails that get good engagement and low complaints, you build a solid reputation; if you send emails that bounce, generate spam reports, or spur unsubscribes, your rep suffers. Mailbox providers use this reputation to decide if your next email should land in the inbox, the Promotions tab, the spam folder, or be blocked entirely. Key components of reputation include your spam complaint rate, bounce rate, how often you send, and how people interact with your messages. Google’s Postmaster Tools, for instance, will show you if your domain’s spam rate is within acceptable range. (Google recommends keeping spam complaints under 0.1% of messages, and says hitting 0.3% or higher is a red flag.) You can monitor a proxy of your reputation via third-party metrics like Sender Score (a 0–100 score available free from Validity’s SenderScore.org). The takeaway: every email you send can either hurt or help your sender rep, so always aim to send wanted, quality emails. A great reputation is like having a golden passport through spam filters.
List Quality & Hygiene:
The quality of your email list plays a huge role in deliverability. Sending to bad addresses, spam traps, or disinterested recipients will torpedo your inbox placement. Unfortunately, many marketers don’t maintain good list hygiene – only 23.6% of businesses verify their email lists before every campaign, according to a recent Kickbox deliverability report. That means nearly 3 out of 4 senders risk hitting dead addresses or spam traps each time they send. It’s vital to clean your list regularly: remove hard bounces (invalid emails), weed out spam trap addresses (signs of an old, scraped, or purchased list), and suppress chronically unengaged subscribers. An important (and often overlooked) hygiene step is verifying new addresses collected via web forms – roughly 9% of emails entered on web signup forms are invalid (typos, fake addresses, etc.). In other words, 1 in 10 potential subscribers might never receive your emails unless you catch those errors. Using an email verification tool (like Kickbox, ZeroBounce, NeverBounce, etc.) to validate addresses can dramatically reduce bounces and improve deliverability. Good list hygiene also means no purchased lists – ever. Buying a list of emails or scraping contacts is a recipe for spam complaints and trap hits (nearly 1 in 10 marketers admitted to purchasing lists in the past two years, a risky practice that often ends badly). Stick to organic, opt-in subscribers and keep your data clean; it’s the foundation of inbox success.
Subscriber Engagement:
These days, engagement is king in the eyes of mailbox providers. Simply put, if the people you email open, read, and click your messages (and don’t ignore or delete them, or worse, flag them as spam), providers will deliver more of your mail to them. Engagement signals – things like open rate (with the caveat of Apple’s privacy changes), click-through rate, reply rate, and how long an email is opened – feed the algorithms that decide placement. Low engagement can even cause your future emails to be filtered out as “low priority” or spam. One major inbox provider, Gmail, is known to use engagement as a factor in sorting mail into the Primary vs. Promotions vs. Spam tabs. The logic is simple: if users consistently don’t engage with your emails, Gmail will assume they don’t really want them. On the flip side, high engagement boosts your sender reputation and inbox placement. This is why relevance is the golden rule: as deliverability experts sum it up, “DO NOT SPAM. Send relevant content to people who’ve said they want to hear from you.” If you focus on content that subscribers find valuable, you’ll naturally get better engagement and fewer spam complaints – and your deliverability will rise. Engagement is also why inconsistent sending can hurt (more on that in a moment): if you only email people once in a blue moon, they might not remember you and could ignore or mark the next email as spam out of confusion. So, cultivate an active, engaged list through great content and regular interaction.
Sending Consistency and Frequency:
Spammers tend to behave erratically – blasting huge volumes, then disappearing, then changing senders, etc. Legitimate senders are more consistent. Mailbox providers notice these patterns. It’s wise to send at a regular cadence and in consistent volumes, rather than sporadic large blasts. For example, instead of dumping 100,000 emails on your list once a quarter with long silences in between, you’d be better off breaking that into more frequent, smaller sends (say 25k emails weekly). If you’re ramping up a new IP address or domain, be sure to “warm it up” gradually – don’t jump from 0 to 1 million emails overnight. Warming up means gradually increasing your send volume over a few weeks, giving mailbox providers time to observe positive engagement and build trust in your new sender identity. “If you have a dedicated IP, 100% you need to be warming it up,” advises email expert Cynthia Price, noting that sending big volumes from a cold IP is a giant red flag reminiscent of spam runs. Think of it as feeding a baby: “Feed a little wanted mail at first, growing that volume over time,” adds another industry veteran. “You’re spoon-feeding the baby… let [the mailbox] digest it and understand it’s not going to hurt them or their users.” In short, establish a reliable sending pattern. Also, consider implementing an email preference center so subscribers can choose how often they want to hear from you (e.g. weekly, monthly, only big announcements). This way your super fans can get frequent updates, while others can opt for lighter touch – preventing you from over-mailing folks who might then hit “spam” or unsubscribe. Consistency + respecting subscriber preferences = healthier deliverability.
Content and Spam Triggers:
What you put in your emails – from subject line to body content – can influence deliverability as well. Spam filters still look at content for red flags. Gone are the days of needing to avoid every use of the word “Free,” but blatant spammy language can hurt at the margins, especially when combined with other factors. A recent analysis of spam emails by ZeroBounce identified the top 10 “most dangerous” spam trigger words – unsurprisingly, they’re all related to money (the list includes terms like “bonus,” “cash,” “income,” “double your,” and of course “free”). This doesn’t mean you can’t ever mention money or use these words if they’re relevant – but be aware that a subject line screaming “Cheap $$$ Deal!!!” raises immediate red flags. Misleading subject lines or from-names are also a fast track to spam folder and regulatory trouble. Aim for clear, honest, and relevant content. Also, consider the format: a message that is one giant image with little text, or a very code-heavy HTML, might get filtered. Likewise, if you send an email with no content (like a blank message or just a single link), filters may assume it’s a phishing test or error. It’s good practice to have a balanced text-to-image ratio and include a plain-text version of your email as backup. One more content factor: make sure you include a visible unsubscribe link in every email and honor opt-outs promptly. Gmail and Yahoo now mandate easy one-click unsubscribe processes for bulk senders. “No more trying to hide the unsubscribe link or sending people to a phone number to opt out,” says Price – such tactics will only increase spam complaints and get you in hot water. Instead, make unsubscribing painless. It’s better to lose a subscriber gracefully than to have them so annoyed they report you as spam, which hurts your reputation with everyone.
Infrastructure and Compliance:
Lastly, a quick grab-bag of other factors: sending infrastructure (e.g. are you using a reputable ESP with proper protocols? Is your sending IP on any blocklists?), regulatory compliance (are you following laws like CAN-SPAM, CASL, GDPR regarding consent, identification, and opt-outs?), and branding measures like BIMI. BIMI (Brand Indicators for Message Identification) is a newer standard where you publish a record that, once you’re authenticated and have a verified trademark, displays your brand’s logo in recipients’ inbox list as a trust indicator. Gmail and others have adopted BIMI, and in 2023 Gmail even added a blue checkmark for BIMI-verified senders – now visible on Android and iOS Gmail apps as well. This doesn’t directly boost deliverability in terms of filtering, but it can improve open rates and user trust (and a highly trusted sender is less likely to ever be marked spam). Similarly, Apple announced a new “Branded Mail” feature that will let verified businesses show brand names and logos in the Apple Mail app later this year. These are worth exploring as they roll out – think of them as ways to visibly prove to users that your email is legitimate and safe to open. In short, ensure all the technical ducks are in a row (correct DNS records, proper sender info, compliance with rules) – it all creates the backdrop for your deliverability success.
By focusing on these key areas – authentication, reputation, list hygiene, engagement, consistency, content, and technical compliance – you cover the bases of good deliverability. It sounds like a lot, but if you notice, it basically boils down to following best practices and treating your subscribers with respect. Next, let’s look at some of the common mistakes marketers make that undermine deliverability (often without realizing it), and how to fix them.
Common Mistakes Marketers Make (and How to Fix Them)
Even seasoned marketers can slip up on email deliverability. Let’s shine a light on a few frequent mistakes that hurt inbox placement, and discuss how to remedy each:
Treating Email as a “Blasting” Tool of Last Resort:
Many brands still use email as a blunt instrument – whenever sales are low or deadlines loom, someone yells “Just send another email to the list!”. This reactive, one-size-fits-all blasting is a mistake. It often means messages with little segmentation or strategy, sent to people who may not be interested, which leads to fatigue and spam complaints. As email expert Kath Pay observes, too many marketers fire off emails simply because “it’s easy” or that’s how they were taught, without recognizing email’s true power. Fix: Flip the script and treat email as a strategic channel, not a dumping ground. Plan campaigns with your audience’s needs in mind. Send emails because they have value to the recipient, not just because you need a quick boost. By elevating email to a well-planned part of your marketing strategy (with proper segmentation, personalization, and timing), you’ll avoid the spammy blast mentality and see better results. And importantly, get buy-in from higher-ups on this approach – sometimes the pressure to “just send more email” comes from execs who don’t understand email marketing. Make the case that less can be more, and quality beats quantity for deliverability and long-term revenue.
Making Newsletters All About You (Not the Subscriber):
A very common mistake, especially in B2B marketing, is filling email newsletters or updates with inwardly focused content – your company news, your new hire announcements, your award press releases – that the subscriber doesn’t care about. As email strategist Jeanne Jennings points out, if your newsletter is “all about you, you’re doing it wrong.” It provides little value to the reader and can tank your engagement metrics. Jennings shared a case study of a B2B company that added a prominent “about us” story (announcing a new partnership) at the top of their client newsletter. The result? The version that led with this self-focused piece saw a 25% lower click-through rate and 41% higher unsubscribe rate than usual – the worst performance since the newsletter’s launch. Meanwhile, the version of the newsletter that put customer-relevant, non-promotional content first did not see those drops. This stark example shows how too much promotional or irrelevant content can quickly alienate subscribers. Fix: Flip the perspective. Curate your email content based on what subscribers find useful or interesting, not just what your company wants to say. Aim for at least a 60/40 balance (or better) between editorial/value content and promotional content in newsletters. That means at least 60% of the email is helpful information, educational resources, industry news, tips, how-tos, case studies, etc. that don’t require a purchase – and at most 40% is directly about your products, offers or company updates. Many successful newsletters stick to 70/30 or even 90/10 in favor of value content. By consistently delivering useful insights, you build trust and engagement, which in turn boosts deliverability for your promotional sends too. And if you do include “all about us” news (new hires, partnerships), tuck it lower down in the email once you’ve delivered other value, or consider if it’s better suited for a press release or blog that interested folks can click through to. Always ask: “Does this piece of content help the reader in some way?” If not, rethink it. The more your subscribers feel your emails are about them, the more they’ll open and interact – keeping your sender reputation healthy.
A B2B newsletter case study: The “Client Version” (right) that led with an 'all about us' partnership announcement saw a -25% lower click-through rate and +41% higher unsubscribe rate compared to its median performance, whereas the “Prospect Version” (left) – which put customer-centric content first – avoided those declines. This illustrates how overly self-promotional content can hurt engagement and drive subscribers away, ultimately harming deliverability.
Neglecting List Hygiene and Permission Practices:
We touched on list hygiene earlier because it’s so vital – yet a lot of marketers fall short here. Whether due to pressure to keep list sizes high or simple oversight, failing to regularly clean your list is a big mistake. Sending to a bunch of inactive or invalid addresses will produce bounces (hurting your stats) and could hit spam traps (hurting your sender reputation). The Sinch/Mailgun “State of Email Deliverability” survey found 39% of senders rarely or never conduct list hygiene – a startling figure. Additionally, some marketers still rely on purchased lists or scraped emails to try to expand reach; as noted, nearly 1 in 10 admit to doing this recently, despite the practice being strongly correlated with deliverability woes. Fix: Make list hygiene a routine part of your email program. Use tools or services to validate addresses (especially before a big send or as new emails come in). Remove or win back inactive subscribers – if someone hasn’t opened or clicked anything in 12 months, it may be time for a re-engagement campaign or a goodbye. And absolutely avoid buying lists; instead, build your audience through opt-in tactics (content offers, events, etc.). It’s better to have a smaller list of engaged, real people than a gigantic list full of ghosts and spam traps. Quality > quantity. Also, ensure you have proper permission for every contact (which is legally required in many jurisdictions anyway). Some marketers get in trouble by emailing old lists of people who technically opted in eons ago but haven’t heard from the brand in years. If you’re reactivating an old list, do it cautiously and perhaps via a reconfirmation opt-in. In 2025, with inbox providers watching engagement like hawks, a smaller active list will out-deliver a big stale list every time.
Failing to Monitor Deliverability Signals:
Many marketers operate on autopilot – they send campaigns and look at open or click rates, but don’t actively monitor deliverability metrics like spam complaints, inbox placement rates, or blocklist status. This is a mistake because you can’t fix what you don’t see. Shockingly, 70% of email senders do not utilise tools like Google Postmaster to monitor their sender reputation with mailbox providers. More than half aren’t monitoring public blacklists for their IPs/domains. Essentially, a lot of teams are flying blind until something implodes (e.g. open rates suddenly plummet because emails are going to spam). Fix: Set up a basic deliverability monitoring regimen. For starters, get access to Google Postmaster Tools (it’s free – you just need to prove you own your sending domain by adding a DNS record). GPT will show you Gmail-specific health indicators: reputation (good/medium/bad), spam complaint rate, etc. Likewise, familiarize yourself with Microsoft’s SNDS (Smart Network Data Services) for Outlook/Hotmail reputation if applicable. There are also free lookup tools to see if your IP or domain is on major blocklists (Spamhaus, etc.) – it’s worth checking periodically or using a service that alerts you. If you use a dedicated IP, consider services like Validity’s Everest, Inbox Monitor, or other deliverability platforms that offer more comprehensive tracking (some ESPs provide these features too). At minimum, watch your bounce logs for signs of blocks (e.g. SMTP error codes that indicate a block or throttling) and pay attention to any sudden changes in engagement metrics by ISP (many ESPs report open/click by domain, so you might notice, for example, Gmail opens crater while others remain fine – a telltale sign of a Gmail filtering issue). In short: keep one eye on deliverability health at all times. It’s much easier to course-correct early than to recover from a full-blown blocklist incident or a tanked sender reputation (which can take weeks or months to rebuild).
Sending at the Wrong Frequency (Either Too Much or Too Little):
Striking the right balance in email frequency is tricky, and missteps here can hurt deliverability. Email too often, and you annoy subscribers into unsubscribing or marking you spam; email too infrequently, and recipients forget who you are (also leading to deletes or spam flags when you finally do reach out). Both extremes are problematic. American consumers in particular have a hair-trigger for opting out: 44% of Americans say they’ll unsubscribe if they get just 1–3 emails from a company in a month that they weren’t expecting, and over 50% will unsubscribe if they get 4+ emails in a month. That’s higher than the global average, indicating U.S. audiences are especially sensitive to frequency. On the flip side, as mentioned earlier, about 30% of B2B marketers don’t even email their prospects once a month – which is so infrequent that it fails to build any brand awareness or relationship. Fix: Calibrate your send frequency to balance staying top-of-mind with not overwhelming people. A good rule of thumb is to send at least one email per month to keep the connection warm (any less and people may not remember subscribing at all). In fact, one marketing survey suggested if you want to maintain brand awareness, you should email at least monthly – and more is often better, as long as it’s relevant. However, going beyond one email per week for general communications can enter the danger zone unless you have a very engaged audience or multiple distinct content streams. Use a preference center to let subscribers choose frequency (e.g. “weekly digest” vs “monthly highlights”). And monitor your unsubscribe and complaint rates – if they jump, that’s a sign you might be sending too often or sending content that’s not meeting expectations. Remember, consistency matters: if you suddenly increase frequency out of the blue, you might spook people. Ramp up gradually and perhaps give a heads-up (e.g. “We’ll be sharing two updates per week during the holiday season to keep you informed of special deals – hope you enjoy!”). Consistency and subscriber-controlled frequency will help ensure you’re emailing just right – not too hot, not too cold.
Ignoring Mobile Optimisation:
This one is an execution mistake that can indirectly affect engagement and deliverability. In 2025, a huge portion of emails are opened on mobile devices – people check emails on their phones at home, on the go, and especially during leisure/vacation periods. If your emails aren’t mobile-friendly (e.g. they require pinching and zooming, or have tiny buttons that are hard to tap), many recipients will simply close or delete them. Low engagement ensues, which can ding your sender reputation. Fix: Always use responsive, mobile-optimized email templates. This includes readable font sizes, a single-column layout (or a design that gracefully rearranges on narrow screens), and touch-friendly buttons/links. It’s also wise to keep your email content concise and “light” – people scanning on mobile don’t have patience for a novel. During certain seasons (like summer), folks are away from their desks and more likely to check email on a phone or tablet, so mobile optimization is extra critical then. Test your emails on multiple device sizes. A good user experience on mobile leads to more engagement – which, as we know, leads to better deliverability. (Bonus: mobile-friendly emails also tend to be more accessible for users with disabilities, which is another important aspect of good email practice.)
Letting Your Sales or Other Teams Undermine Your Sender Reputation:
Sometimes the threat to your deliverability comes from inside your organization. A common scenario: the sales team starts using a tool to send “semi-personalized” cold emails to prospect lists. Those emails might be sent from the same domain as your marketing emails. If the sales folks blast out poorly targeted messages that generate spam complaints, your whole domain’s reputation can suffer, hurting deliverability for all departments. This isn’t to blame sales – outreach is part of business – but if done without coordination, it can cause issues. Fix: Align with any team sending bulk or automated emails (sales, customer success, etc.) on best practices. Ensure they’re following the same opt-in and relevance principles as marketing. It may even be wise to use a separate sending domain or IP for sales emails, so that if their activities generate a bit of heat, it doesn’t scorch your main marketing domain. For example, use sales.yourcompany.com for outreach tools and keep news.yourcompany.com for marketing newsletters. That way reputations are segregated. Also, educate your colleagues: spam rules and deliverability apply to all email. Sales should avoid purchased lists too, and make sure their content is highly relevant if it’s cold outreach (or else send very small, truly one-to-one messages which typically don’t trigger filters). Many sales engagement platforms include settings to stagger sends and personalize emails – use them to avoid sudden surges that look spammy. Internal coordination here can prevent the “left hand” from inadvertently ruining what the “right hand” is building in terms of sender reputation.
Those are some of the biggie mistakes, but certainly not an exhaustive list. Overall, the theme is: be subscriber-centric and vigilant. Don’t take shortcuts like buying lists or hiding unsub links. Don’t default to “blast mode” or neglect proper maintenance. If you avoid these pitfalls, you’ll fix a lot of deliverability problems before they start.
Now, let’s talk about something seasonal that often perplexes marketers – the summer doldrums – and how to adapt your email strategy without hurting deliverability.
Seasonal Trends: Surviving the Summer Email Engagement Slump
Have you ever noticed your email metrics dip in the summer months? You’re not imagining it. Seasonal trends play a role in email engagement, and summer is famously a slow period for many industries. People are on vacation, outdoors, or simply less tied to their work devices – which can mean lower open rates and click rates from June through August. For B2B companies, summer often means more out-of-office auto-replies and delayed responses. In fact, data from ZoomInfo shows that mid-June through August is the worst season for reaching people at work, with an average out-of-office (OOO) rate around 3% (vs. a 2.7% median annually). The week of July 4th, for example, has one of the highest OOO rates of the year (over 4%), second only to the Christmas/New Year’s holiday week (which spikes to nearly 7% OOO). So yes, summers can be tough for email engagement – but that doesn’t mean you should hit the “pause” button on your email marketing.
Here’s how smart marketers are adapting to seasonal lulls like summer, to keep deliverability and engagement strong year-round:
Don’t Go Dark – Maintain a Baseline of Communication:
It’s tempting to scale back or stop emails in summer if you see engagement dropping. But do not completely disappear for three months – that can actually harm your deliverability because your list goes cold. Consistency is still important. Marketing experts advise continuing to send at least some emails regularly, even during slow seasons, to maintain brand awareness and sender reputation. Think of it as “staying in touch” so that when fall comes and people refocus, you haven’t been forgotten (or worse, you don’t suddenly send a big blast after months of silence – which can trigger spam filters and confuse recipients). You might reduce frequency a bit, but at minimum try to send at least one email per month over the summer to each segment. That keeps your authentication warmed up and your audience remembering who you are.
Optimize for On-the-Go Reading:
In summer, your audience may be at the beach or pool – not chained to a desktop. That means they’re more likely to check email on mobile devices during spare moments. So double down on mobile-friendly design (if you haven’t already). Make sure your emails look great on a smartphone screen: concise copy, bold headlines, easy taps. Also, consider the context – someone relaxing on vacation might appreciate a lighter, more visual email than a text-heavy whitepaper download (which they’ll probably skip until they’re back at work). For B2C, summer might be prime time for emails with bright imagery, a breezy tone, or even a summer sale theme. For B2B, maybe lean into infographics or quick tips that are easy to consume on the go. The key is to meet your subscribers where they are (literally, on their phone under an umbrella!).
Keep It Light and Relatable:
Summer is a unique season, culturally. People’s mindsets shift – often they’re a bit more relaxed or distracted. Align your content accordingly. This could mean injecting some summer personality into your campaigns (e.g. subject lines referencing summer fun, or content that acknowledges your reader might be in “vacation mode”). Also, summer might not be the time for your heaviest, most serious content. You might save that 40-page research report or detailed product pitch for September, and instead use summer emails to nurture with lighter content – think “Top 5 reading list for the beach (courtesy of [Your Company])” or a customer story that’s inspiring yet easy to read. The idea is to stay relevant to subscribers’ lives right now. An email that feels out of sync with the season (“Work 24/7! Hustle hard!” in mid-July) might get ignored or irritate people. Conversely, an email that resonates (“We know it’s summer – here’s something enjoyable and useful for you during the slow season”) can keep them engaged with your brand. Keeping the tone personable and the content digestible will encourage subscribers to continue opening even when they’re in a summer state of mind.
Adjust Send Times and Days:
Consider experimenting with your send schedule during seasonal shifts. If you always send at 8 AM on Mondays, that might work great in winter when folks are at their desks, but in summer, maybe a lot of your audience is slower to start on Mondays (or extending weekends). You might try sending emails at different times to “catch” people when they do check messages. For instance, possibly later in the morning or even early evening when vacation-goers are back from the day’s activities. Some B2C brands find that weekend emails perform better in summer than they do other times of year, since consumers may actually browse personal emails on a lazy Sunday afternoon (whereas during a busy fall, weekday evenings might be better). Use any data you have – if you notice your open rates shifting an hour or two later in the day during summer, follow that trend. The goal is to match your sending to subscriber routines. Also, watch which days get the best engagement. Perhaps mid-week emails dip in July because many people take long weekends – so maybe try a Wednesday or even a Sunday send. Every audience will differ, but the point is to be flexible with timing when you see seasonal behavior changes. (Just remember to monitor results carefully; you don’t want to permanently move to a worse time based on an anomaly. Test and compare.)
Plan for Re-engagement Post-Summer:
Accept that summer may have lower engagement and plan a nice re-engagement or ramp-up campaign for the fall when people are back in work mode. Early September (or late August) is a great time to send a “Welcome back from summer, here’s what you missed” type of email, or a series of high-value emails to wake up anyone who went a bit dormant. This can help refresh your list’s interest and also scrub out those who really aren’t interested anymore. By proactively re-engaging, you signal to mailbox providers that your list is active and cared for, heading into the crucial end-of-year season for many businesses.
One more thought: Don’t panic if summer numbers dip. It’s often seasonal and not a verdict on your strategy. The important thing deliverability-wise is to avoid drastic reactions like blasting more to “make up” for low opens (which can backfire) or stopping sending altogether. Instead, ride the wave with a steady, thoughtful approach, and you’ll come out the other side with your sender reputation intact or even strengthened.
Tools and Tactics to Monitor & Improve Deliverability
Improving email deliverability isn’t a one-time project – it’s an ongoing process. Fortunately, there are many tools and tactics that can make the job easier and give you visibility into how you’re doing. Here’s a toolkit for deliverability management in practice:
Deliverability Monitoring Tools:
As mentioned earlier, set up Google Postmaster Tools for your domain. It’s free and provides insight into Gmail-specific metrics: spam rate, domain reputation (rated from bad to high), feedback loop data, etc. For other providers, check if similar dashboards exist (Microsoft’s SNDS for Outlook, Yahoo’s postmaster page, etc.). Additionally, consider a dedicated deliverability platform or a service from your ESP. Tools like Validity’s Everest (formerly Return Path), 250ok (now part of Validity), Kickbox’s deliverability suite, or SparkPost’s analytics can track inbox placement rates, provide spam trap monitoring, and even run seed list tests (sending to a set of test addresses at various ISPs to see where emails land). If budget is an issue, there are smaller tools like MailTester, GlockApps, or MX Toolbox that offer specific checks (spam score testing, blacklist scanning) on demand.
Email Verification Services:
A key tactic to improve deliverability is to verify and validate addresses before you send. We’ve noted how many brands skip this (only 23.6% verify lists every time), leaving them vulnerable to sending to bad emails. Using an email verification API or service can greatly reduce bounces and spam trap hits. Services like Kickbox, ZeroBounce, BriteVerify, and others can bulk-clean a list or even integrate with your signup forms to validate in real time. This helps remove those ~9% of invalid form entries and any other problematic emails lurking on your list. It’s an easy win: you’ll likely see your bounce rate plummet on the next send, which improves your standing with ISPs. Just be sure to choose a reputable verifier that won’t accidentally remove valid addresses; and remember to suppress addresses that soft-bounce repeatedly or show no engagement for a long period, as those can turn into spam traps.
Reputation Monitoring and Blocklist Alerts:
Your sending platform might alert you if you get blocklisted, but it’s good to independently monitor. Tools like Sender Score (as mentioned, to gauge your IP reputation on a 0–100 scale) or Talos Intelligence (for Cisco’s view of your IP/domain) can be checked periodically. For blacklist monitoring, you can use services such as MXToolbox’s free lookup (manually) or a paid service that continuously checks dozens of blacklists and emails you if you appear. If you do find yourself on a blacklist (e.g. Spamhaus), investigate and reach out to resolve it – sometimes it’s as straightforward as filling out a form after fixing the root cause, other times you might need an expert’s help. Also, keep an eye on spam complaint rates through your ESP (most will show the percentage of recipients who marked a message as spam). If that creeps up near thresholds (e.g. approaches 0.1% of sends at Gmail), it’s a warning sign to adjust your practices.
Email Testing Tools:
Before sending an email to your whole list, use testing tools to catch potential deliverability issues. Many ESPs have a built-in “spam check” or preview that flags things like missing authentication, problematic content, or a broken unsubscribe link. You can also send test emails to yourself across different email accounts (Gmail, Yahoo, Outlook, etc.) to see if anything lands in spam – it’s not foolproof, but it can catch obvious problems. Tools like Litmus or Email on Acid not only show design previews but also test against spam filters and provide a deliverability score. Gmail’s new features (like the promotion tab annotations or schema markup for inbox actions) and Outlook’s Focused Inbox make the landscape complex – reading up on their latest updates (for instance, Gmail’s new summary cards for promotions) can give you an edge in crafting emails that inboxes favor. Gmail’s summary cards, which show key info like package tracking or event details at a glance, are a good example: they aim to improve user experience, and emails that make use of these dynamic, value-adding elements might see better engagement and fewer spam complaints. While implementing such advanced features might be overkill for a small business, being aware of them is useful. At minimum, always do a test send and open your own email on multiple devices to ensure everything loads quickly and correctly – a broken email won’t get engagement, and no engagement = deteriorating deliverability.
Engagement Analytics & Segmentation:
Use your email analytics to your advantage. Identify your highly engaged subscribers and consider sending to them more frequently or first (ISP algorithms often gauge how a sample of your list reacts, so if you initially send to your most active fans, you may get a burst of positive engagement that “primes” the ISP to treat the rest of the send more favorably). Likewise, segment out chronic non-responders and either suppress them or try a reactivation campaign separately. Many marketers implement a sunset policy: e.g. if someone hasn’t opened or clicked in 6-12 months, they get a “We miss you – do you still want our emails?” message. If no response, you stop mailing them. This kind of list management keeps your active engagement rate high and your complaint rate low. Yes, it can be hard to let go of emails from your list, but emailing large numbers of disinterested people will hurt you in the long run. It’s better to have 10,000 engaged readers than 100,000 who mostly ignore you. Engagement-based segmentation is a powerful tactic to improve deliverability by essentially only sending to those likely to engage. Just be careful: if you overly silo your list, you don’t want to accidentally never attempt to re-engage lapsed subscribers. A good approach is a tiered one – like A/B test a reactivation subject line on a small cohort of unengaged folks and see if you can win some back without tanking metrics.
Use a Preference Center & Easy Opt-Down:
Another tool in your kit is an email preference center page where subscribers can manage their subscription. We touched on this in mistakes, but in terms of deliverability improvement, a preference center can reduce spam complaints. How? It gives people an alternative to hitting the “Spam” button when they feel they’re getting too much email. If the unsubscribe link in your email leads to a page where they can choose “Receive emails less often” or “Only get product updates, not newsletters,” some folks will take that route instead of leaving entirely or reporting spam. That keeps them on your list (in a way that suits them) and avoids a complaint. Setting up a good preference center (with options for frequency, content types, and a clear way to fully unsubscribe too) is a one-time effort that can pay ongoing dividends in subscriber happiness and deliverability.
Authentication & Certification Tools:
We discussed SPF/DKIM/DMARC – ensure those are monitored. DMARC reports (which you can receive by email if you have a DMARC record with a reporting address) are a tool themselves: they can tell you if someone is spoofing your domain or if legitimate sources aren’t authenticated properly. Consider using a DMARC monitoring service or aggregator (many free ones exist) to parse those XML reports and alert you of issues. If you’re a really high-volume sender, there are also certification services (like enrollment in certain allow lists or services like Return Path Certified, now part of Validity, historically) which, if you meet strict criteria, can slightly improve how your mail is treated. Those aren’t necessary for most, but it’s good to know they exist.
Feedback Loops:
Major ISPs (like Yahoo, Microsoft, AOL, Comcast, etc.) offer what are called feedback loops (FBLs) for senders. When a recipient at those ISPs marks your email as spam, the FBL will ping you (or your ESP) with a report so you can remove that person from your list proactively. Many ESPs handle FBLs for you (i.e. they auto-suppress anyone who clicks “report spam” and share aggregate counts). But if you manage your own sending, you should sign up for these loops. They’re a useful tool to literally “hear” when someone complained. By processing FBL reports, you can get complainers off your list immediately (which is good hygiene) and possibly identify if a certain campaign caused higher complaints than usual – a sign something in that email or audience targeting was off.
Consultants and Community Resources:
If deliverability issues persist or you’re dealing with a complex situation (like migrating to a new ESP or IP, or a sudden block you can’t resolve), don’t hesitate to seek expert help. There are email deliverability consultants who can analyze headers and logs and pinpoint issues. But also, there’s a strong email geek community – places like the EmailGeeks Slack channel, or forums on Only Influencers, Litmus community, etc., where you can ask questions. Often, someone else has faced a similar challenge. Staying plugged into industry blogs (MarTech, Email on Acid, Litmus, etc.) can keep you updated on changes – such as “iOS 18 introduced new inbox categories,” or “Google is experimenting with ‘Shielded Email’ aliasing” – all of which can indirectly affect marketing tactics. Consider this part of your toolkit: knowledge and network.
Using these tools and tactics will make improving deliverability much more systematic. Instead of guessing, you’ll have data and diagnostics. Instead of reacting to a crisis, you’ll catch issues early or prevent them. It’s a bit like maintaining a car – regular tune-ups and using the right instruments to check the engine will keep you from breaking down on the highway.
Finally, let’s talk about mindset – specifically, how to test and learn your way into continuously better email performance, and how to treat failures as opportunities rather than disasters.
Embrace Testing (and Failure) to Continuously Improve
Even with all the best practices in place, email marketing is part art, part science. Not every campaign will be a home run. You will inevitably have some flops – a creative that didn’t resonate, a subject line that tanked, or a new tactic that backfired. The key is how you respond and learn from those failures. In fact, many top marketers argue that marketing success requires a dose of failure. Testing and occasional failure are how you discover what works and what doesn’t.
If you’re not regularly testing your email program, you’re likely leaving improvement on the table. A/B testing subject lines, content, send times, segmentation strategies – this is how you inch your way to higher engagement and better deliverability over time. But a mistake some make is giving up on a test as soon as they see one failure. For example, a team might say, “We tried sending a newsletter at 6pm once, and it didn’t work – so we won’t try that again.” Or “We tested a playful subject line and open rate went down, so no more humor in subject lines.” This cautious approach can stifle progress. As email veteran Ryan Phelan notes, “We tested that once and it didn’t work” is a common refrain – and it’s misguided. One test is not the final answer. “If I gave up every time an email test didn’t work, I’d be unemployed permanently,” Phelan quips. The reality is that tests are supposed to sometimes fail – that’s how you learn.
Here are some tips on fostering a testing culture and learning from failures:
Always Be Testing Something:
Approach your email program as a laboratory. Each campaign is an opportunity to learn. Even if it’s just a subject line split test, have a hypothesis and see what happens. If it “fails” (i.e. the challenger does worse than the control), you still learned something about your audience’s preferences. And don’t just test the easy stuff like subject lines forever. Yes, subject lines are the simplest A/B test and can yield quick wins, but as Phelan says, “your subject line is just one component of your email, and your message is one component of your campaign.” Limiting testing to only that is like only tuning one string on a guitar. Try bigger, bolder tests occasionally – like a whole new design vs. the standard, or a different cadence, or a new segmentation approach. Those larger tests carry more risk of a “failure,” but also potentially bigger insight.
Treat Failed Tests as Stepping Stones:
When a test results in a negative outcome (e.g. variant B got fewer clicks than A), don’t see it as wasted effort. Instead, analyze why. Was the new subject line actually not compelling, or could it be that the segment you tested on wasn’t the right audience for it? Maybe test it again on another segment or tweak the idea. “If a test fails, run it again. Try to see if you can replicate the failure,” advises Phelan. “This ensures your result isn’t a fluke. Then evolve it based on what you learned.”. The point is, a single data point isn’t the full story. Perhaps your hypothesis was right but the execution was slightly off. Or maybe the hypothesis was wrong, and now you pivot to a new idea. In either case, document these learnings.
Create a Culture Where It’s Safe to Fail (Within Limits):
Often, the barrier to testing is a fear of failure – sometimes personal, sometimes coming from a boss who doesn’t want to see a dip in metrics. It’s important to communicate that controlled tests are not the same as catastrophic mistakes. A dip in one metric for one email is worth it if it teaches how to improve future emails. Encourage your team (and management) to view tests as investments in knowledge. One way is to keep tests limited in exposure until you’re confident. For example, roll out a test to 10% of the list – if the new idea bombs, 90% of recipients still got the standard version, minimizing harm. If it succeeds, you can then send the winning version to the remaining 90%. This kind of approach (common with subject line testing in many ESPs) allows for failure without high cost. Internally, celebrate the learnings from tests, not just the wins. If a test showed that your audience hates a certain phrasing, that’s great to know! You just saved your team from using that approach in a big campaign.
Analyze and Iterate:
After each campaign (or at least on a regular cadence), do a mini retro. Look at what went well and what didn’t. If an email had unusually high unsubscribes or spam complaints, dig into why. Was it the content, the segment, the send time? Use surveys or focus groups if needed – when was the last time you asked a subset of your subscribers for feedback on your emails? Jennings suggests even interviewing subscribers or conducting a survey to see what they want in a newsletter. That insight can be gold for guiding tests. The idea is to close the loop: failure -> feedback -> adjustment -> try again. Over time, this cycle will significantly improve your outcomes.
Plan for Failure Recovery:
Sometimes a campaign will just flop outside of a test scenario – say a big send on Black Friday goes to spam more than expected, or a broken link hurt your conversion. Have a mindset of resilience. If a critical email fails (in content or deliverability), you can often recover: resend a corrected version with an apology if needed (just be careful not to make a habit of it), or follow up with those who didn’t engage with a “we noticed you missed this, here’s another chance” type of email. As long as you don’t overdo it, ISPs generally won’t penalize one-off corrective sends. More importantly, do the post-mortem: figure out what went wrong technically or strategically, and document that to avoid repeating it. This is how you build a robust program.
There’s a great anecdote Phelan shares from earlier in his career: he made a mistake that got the CEO’s attention – a big failure that could have gotten him fired. Instead, the CEO asked, “What did you learn?” Phelan answered, and the CEO said, “I don’t care that you failed. Just don’t do it again.”. That perspective is invaluable. Mistakes will happen – the key is to ensure they happen only once. If you take the lesson to heart and improve, your marketing gets stronger. As Phelan concludes, “Look for lessons from both your successes and failures… I learned that you have to look inward... that self-reflection – and overcoming the fear of failure – can shape every aspect of your experience.”.
So, embrace the iterative process. By continually testing, learning, and optimizing, you’ll not only improve engagement but also fine-tune your deliverability. Why? Because many deliverability boosts come from figuring out exactly what your audience responds to and giving them more of that (and less of what they dislike). Through testing, you might discover certain content topics that drive lots of clicks – and hey, more clicks means ISPs see folks love your mail. Or you might find a format that gets less engagement – and you stop using it, avoiding those disinterested responses that could hurt your reputation. In essence, constant improvement via testing is like regularly updating a recipe until it’s just right – and mailbox providers “taste” the end result through engagement metrics.
Conclusion: Deliverability as a Growth Driver
It’s clear that in 2025, email deliverability is no longer a niche technical topic – it’s central to marketing success. If you’ve made it this far, you’ve gained a journalist’s view into the strategies and tactics that separate inbox winners from spam folder losers. From getting your authentication in order, to maintaining a squeaky-clean list, to crafting subscriber-centric content and adjusting to seasonal behaviors, it all adds up to one goal: earning your place in the inbox.
Remember, email isn’t just a channel to push promotions; it’s, as Kath Pay eloquently says, “your brand’s most controllable growth lever” when used strategically. An email program firing on all cylinders – with great deliverability, engaging content, and constant optimization – becomes a conversion machine and a loyalty engine for your business. On the flip side, if email is treated as an afterthought, with poor practices, it can quietly bleed revenue (in the form of missed opportunities and customer churn due to frustration).
The exciting part is that improving deliverability often brings immediate, tangible benefits. You’ll see more of your emails getting opened by real people. You’ll likely see your click rates and conversions rise as you purge dead weight and focus on relevance. It’s not uncommon for businesses to experience a significant boost in ROI from email after cleaning up their act deliverability-wise. One study showed average deliverability rates have actually improved globally in recent years – from about 94.2% in 2020 to 96.4% in 2023 – meaning those who follow best practices are enjoying very high inbox placement. You want to be in that cohort of 96% delivered (or higher), not scraping by with 80% and wondering what happened to the other 20% of your emails.
As a marketer or small business owner, you don’t need to be a technical wizard to get deliverability right. You just need a solid understanding (which you now have) and the commitment to implement these strategies. Start with the fundamentals: authenticate your emails, send content people want, clean your list, and monitor your reputation. Avoid the common pitfalls that turn email from a welcome guest into an unwelcome pest. Use the tools at your disposal to keep a pulse on your performance. And foster a mindset of testing and learning, so you continuously get better and adapt to changes (because the email landscape will keep evolving – AI in email, new inbox features, and privacy shifts will provide new challenges and opportunities).
In closing, think of email deliverability as akin to deliverability in the postal world – you want your message to reach the right mailbox, in good condition, at the right time. You control many of the factors that ensure that happens. By applying the insights and best practices we’ve discussed – and maybe sharing a few of these stats and tips with your team – you’ll be well on your way to seeing more of your emails land in inboxes and deliver the results you’re looking for.
Here’s to your emails not being misunderstood or lost, but being opened, read, and acted upon by an audience that’s glad to see them. Master deliverability, and you’ll unlock the full potential of what is arguably the most powerful (and now less misunderstood) channel in your digital stack: email. Happy sending, and may your open rates be ever in your favor!
Sources:
The insights and examples in this article were drawn from a variety of expert sources, including the MarTech 2025 deliverability guide, industry reports like the Kickbox Email Deliverability Benchmark, email strategists’ columns on MarTech, and seasonal marketing tips from Canadian Business/Cyberimpact’s team, among others. These references (noted throughout with the 【†】 citation format) provide a wealth of additional reading for those who want to dive deeper into each topic. By learning from these real-world studies and expert recommendations, you can confidently navigate the ever-changing email landscape and keep your campaigns thriving in the inbox.