You can write the best email in the world, but if it lands in spam, nobody reads it. Email deliverability—the ability of your emails to actually reach the inbox rather than getting filtered, blocked, or bounced—is the unglamorous foundation that everything else in email marketing depends on. Your open rates, click rates, conversions, and revenue from email all start with one question: did the email arrive? Here’s how to get deliverability right and keep it right.
Understand what affects your deliverability
Deliverability isn’t determined by a single factor—it’s the result of multiple signals that mailbox providers (Gmail, Outlook, Yahoo, Apple Mail) evaluate to decide whether your email belongs in the inbox, the promotions tab, the spam folder, or the reject pile.
Your sender reputation is a score that mailbox providers assign based on your sending behaviour over time—complaint rates, bounce rates, engagement patterns, and sending volume consistency. Authentication is whether your emails are properly verified as actually coming from you rather than someone spoofing your domain. Content quality covers what’s in the email itself: structure, text-to-image ratio, link quality, and whether it triggers spam filters. List hygiene is about who you’re sending to—whether they’re valid addresses, whether they’ve consented, and whether they actually want to hear from you. And engagement metrics—whether recipients open, click, reply, or mark you as spam—are increasingly weighted by providers like Gmail to determine inbox placement.
These factors interact with each other in complex ways. A great email sent to a dirty list will still get flagged. A clean list won’t save you if your authentication is broken. And strong authentication doesn’t matter if your content consistently triggers spam filters. You need all of them working together.
Set up proper authentication
If you haven’t configured SPF, DKIM, and DMARC records for your sending domain, do it now. These are the three authentication protocols that prove to receiving servers that your emails actually come from you and haven’t been tampered with in transit.
SPF (Sender Policy Framework) tells receiving servers which IP addresses are authorised to send email on behalf of your domain. It’s a DNS record that says “these servers are allowed to send as us.” DKIM (DomainKeys Identified Mail) adds a cryptographic signature to your emails that the receiving server can verify, proving the message wasn’t altered between sending and delivery. DMARC (Domain-based Message Authentication, Reporting, and Conformance) ties SPF and DKIM together and tells providers what to do with emails that fail authentication—quarantine them, reject them, or just report them.
All three are table stakes in 2026. Without them, you’re starting at a significant disadvantage. Gmail and Yahoo both announced stricter authentication requirements that make DMARC effectively mandatory for bulk senders. Setting these up requires access to your DNS records and coordination with your email service provider, but it’s a one-time configuration that pays off permanently.
Clean your list regularly
Sending to invalid, inactive, or unengaged addresses hurts your reputation with every send. Hard bounces—emails sent to addresses that don’t exist—should be removed immediately and automatically. Most email platforms handle this, but verify that yours actually does. Soft bounces—temporary delivery failures—should be monitored and addresses removed after repeated failures (typically three to five consecutive soft bounces).
Subscribers who haven’t opened or clicked anything in six months are a harder judgment call. They might be reading without clicking (especially if they use a privacy-focused email client that blocks open tracking). But a large segment of completely inactive subscribers drags down your engagement rates, which signals to providers that your emails aren’t wanted.
Run a re-engagement campaign for inactive subscribers: a direct email asking “Do you still want to hear from us?” with a clear call to action. Those who respond stay. Those who don’t get removed after a final notice. It feels painful to shrink your list, but a smaller, engaged list outperforms a large, disengaged one in every metric that matters.
And never, ever buy email lists. The short-term volume isn’t worth the long-term damage to your sender reputation, the spam complaints from people who never asked to hear from you, and the potential legal consequences under GDPR, CAN-SPAM, and similar regulations.
Warm up new domains and IPs
If you’re sending from a new domain or a new IP address—whether because you’re starting fresh, switching email providers, or adding a dedicated sending IP—you need to build reputation gradually. Mailbox providers are inherently suspicious of new senders because spammers constantly burn through fresh domains.
Start with small volumes sent to your most engaged subscribers—the people most likely to open, click, and not report you as spam. These positive engagement signals build your reputation with providers. Then increase volume gradually over several weeks, adding less-engaged segments as your reputation establishes.
The exact ramp-up schedule depends on your total list size and sending frequency. A common approach is starting with 50–100 emails per day and doubling every few days, monitoring bounce rates and spam complaints at each step. Most email platforms offer warm-up guidance specific to their infrastructure. Follow it. Patience here pays off significantly—blasting 50,000 emails on day one from a fresh domain is a near-guaranteed trip to the spam folder.
Monitor your sender reputation
You can’t fix what you can’t see. Use monitoring tools to track how mailbox providers view your sending reputation, and check them regularly—not just when you notice a problem.
Google Postmaster Tools (free) shows you domain reputation, spam rate, authentication status, and delivery errors for emails sent to Gmail addresses, which likely represent a significant portion of your list. Your email platform’s analytics will show bounce rates, complaint rates, and delivery rates across all providers. Third-party tools like Sender Score or MXToolbox provide additional perspective.
Set up alerts for sudden changes. A spike in bounce rates might indicate a list quality issue. A jump in spam complaints might mean your content or frequency has crossed a line. A drop in domain reputation might signal that something in your sending infrastructure has changed. Catching these early—within days rather than weeks—is the difference between a quick fix and a months-long recovery from a damaged reputation.
Watch your content triggers
Certain content patterns increase the likelihood of spam filtering. Excessive capitalisation (“FREE OFFER NOW!!!”), too many exclamation marks, misleading subject lines that don’t match the email content, image-heavy emails with minimal text (a classic spam pattern), shortened URLs from unknown services, and emails that are essentially one giant image with no readable text content.
None of these are automatic death sentences—context matters, and modern spam filters are more sophisticated than simple keyword matching. But stacking several of these in one email raises flags that individually they might not trigger.
Write emails that look and feel like something a real person would send to someone they respect. Clean design with adequate white space. Clear, readable text that conveys the message even if images don’t load. Honest subject lines that accurately preview the content. A sensible text-to-image ratio (aim for at least 60% text, 40% images). And links that go to legitimate, properly configured domains.
Make unsubscribing easy
This feels counterintuitive—why make it easy for people to leave?—but making it easy to unsubscribe actually improves deliverability. When people can’t find the unsubscribe link (or when it’s buried, tiny, or requires logging into an account), they hit “mark as spam” instead. And spam complaints hurt your reputation far, far more than unsubscribes do.
Include a clear, one-click unsubscribe option in every email. It’s also legally required in most jurisdictions—GDPR, CAN-SPAM, CASL, and PECR all mandate easy opt-out mechanisms. Google and Yahoo now require one-click unsubscribe headers for bulk senders, making this a technical requirement as well as a legal and strategic one.
Think of easy unsubscribing as a pressure valve. It lets uninterested people leave gracefully, which protects your reputation and keeps your remaining list healthier and more engaged.
Segment and personalise
Sending the same email to your entire list means a significant portion of recipients will find it irrelevant. Irrelevant emails get ignored, deleted, or—worst case—marked as spam. Each of those non-engagement signals tells mailbox providers that your emails aren’t valuable to the people receiving them.
Segment your list by engagement level (highly active, moderately active, at-risk), by purchase history or product interest, by expressed content preferences, by how they joined your list, and by where they are in the customer lifecycle.
Many businesses manage these data points inside an eCommerce CRM, which centralizes customer behavior, purchase history, and engagement signals to support more precise email segmentation and lifecycle messaging. Then tailor your content and sending frequency for each segment.
Your most engaged subscribers can hear from you more frequently. Your least engaged subscribers should receive less frequent, higher-value emails. New subscribers need a different onboarding experience than long-time customers. And someone who bought running shoes probably doesn’t want emails about formal wear.
Higher relevance leads to better engagement, which signals to mailbox providers that your emails are wanted, which improves inbox placement, which improves engagement further. It’s a virtuous cycle that starts with treating your subscribers as individuals rather than a single, undifferentiated list.
Maintain a consistent sending schedule
Erratic sending patterns—nothing for three months, then five emails in a week—confuse both mailbox providers and subscribers. Providers flag sudden volume spikes from previously quiet senders as potentially suspicious. Subscribers who haven’t heard from you in months are more likely to forget they subscribed and mark your re-emergence as spam.
Establish a consistent cadence that your audience expects and that you can sustain indefinitely. If you commit to a weekly newsletter, send it weekly. If you promise monthly updates, send them monthly. Consistency builds familiarity, and familiarity builds the trust that keeps you in the inbox.
If you need to increase frequency, do it gradually and monitor the impact on engagement and complaints. If you need to decrease it, that’s usually fine—sending less frequently is rarely penalised unless you go completely silent and then blast your list unexpectedly.
Focus on delivering genuine value
Mailbox providers increasingly look at engagement signals—opens, clicks, replies, and whether recipients move your emails to folders or mark them as spam—to decide where your future emails should land. The easiest way to generate positive engagement signals is simple: consistently send emails that people actually find useful.
Value can take many forms depending on your business: practical tips your audience can apply immediately, early access to product updates, exclusive insights, or relevant offers that genuinely match a subscriber’s needs. When recipients regularly open and interact with your emails because they expect something worthwhile, inbox placement improves naturally.
Referral or advocacy campaigns can also work well when they’re framed as value rather than promotion. For example, some companies invite satisfied customers to recommend the product to friends and reward both sides when a referral becomes a customer. Platforms like ReferralCandy help businesses run these referral programs while making the offer clear and beneficial for subscribers rather than feeling like another generic marketing email.
The guiding principle is simple: if each message gives the reader a clear reason to care, engagement improves—and better engagement is one of the strongest signals mailbox providers use to keep your emails in the inbox.
The ongoing commitment
Deliverability isn’t a one-time fix. It’s an ongoing practice of list hygiene, reputation monitoring, content discipline, and engagement optimisation that needs regular attention as long as you’re sending email. Treat it as a standing item in your email marketing operations: a monthly check-in on reputation metrics, a quarterly list cleaning, an ongoing awareness of content best practices.
The payoff is straightforward: more of your emails reach real people in their actual inboxes. And everything you build on top of that—campaigns, automations, nurture sequences, product launches, re-engagement flows—works better because it’s reaching the audience it’s meant for. Deliverability is invisible when it’s working and devastating when it’s not. Invest in keeping it working.
