That gap between “sent” and “seen” is what email deliverability is all about. You can write an incredible email with a great offer, but it won’t matter if the inbox provider decides not to show it. The good news is that deliverability isn’t luck. It comes down to a handful of things you can actually control, and most of them are fixable. Here’s how we think about it, roughly in the order that tends to move the needle most.
1. It starts with your list, not your email
Before you touch a single word of copy, look at who you’re emailing. List quality is the biggest lever you have, and it’s the one people ignore most.
Inbox providers, Google especially, watch how people react to your messages. When you send to folks who open, click, and reply, your reputation climbs. But when you send to dead addresses and people who stopped caring months ago, your reputation sinks. Keep in mind that annual list cleanup isn’t enough anymore. If you scrub your database once a year, some contacts sit unengaged for twelve months or more before you remove them, and every send to them chips away at your standing. Move to an ongoing process instead. Retire contacts as they go quiet, not on an annual schedule.
And be skeptical of leads from outside sources. A data provider telling you an address is valid is not the same as it actually being valid. Run new leads through a dedicated validation tool such as NeverBounce, Kickbox, or QuickMail before they ever get an email. It’s a small step that prevents a lot of bounces.
If you have contacts that are marketing-suspended or quarantined, keeping them in your database is totally okay, as long as you never send to them. They’re still useful for reporting; just make sure every send excludes them. And be careful with one-off internal experiments or surprise test blasts. They can feel harmless in the moment, but sudden unusual sending leaves a mark on your reputation that sticks around longer than you’d expect.
2. Prove you’re really you
Inbox providers get impersonated constantly, so they lean hard on authentication to decide whether to trust you. These three records do the heavy lifting when it comes to that authentication (with a fourth one worth knowing about too):
SPF (Sender Policy Framework) lists the servers allowed to send email for your domain. It ends in either “-all” (a hard fail) or “~all” (a soft fail). A hard fail tells receivers to reject anything not on the list, which sounds strict and safe but can backfire. If a legitimate sending path isn’t perfectly accounted for, your real mail gets rejected outright. For most marketing setups, a soft fail is the safer choice. It still flags anything suspicious without slamming the door on your own campaigns. If your root domain is on hard fail, switching it to soft fail is a quick, worthwhile change.
DKIM (DomainKeys Identified Mail) adds a cryptographic signature to your emails. It proves the message actually came from you and wasn’t tampered with in transit.
DMARC ties SPF and DKIM together and tells receivers what to do when a message fails those checks. You can set the policy to “none” (do nothing), “quarantine” (send to spam), or “reject” (block entirely). Reject is the strictest, but for marketing sends running through platforms like Marketo, quarantine often performs better. Reject can wipe out legitimate mail the moment any small alignment issue appears, while quarantine gives you a softer landing. One gap people miss is to add a subdomain policy (sp=quarantine). Without it, someone could spoof a subdomain you don’t even use. While you’re in there, add reporting addresses so you can receive DMARC failure reports and catch problems early. It’s worth monitoring those closely for a while, especially right after making changes.
BIMI (Brand Indicators for Message Identification) is the fourth one. It puts your logo next to your emails in supported inboxes, which builds trust and recognition. It requires DMARC set to quarantine or reject and a properly formatted SVG version of your logo. We’d call this a later priority rather than an urgent fix. Sort out your other records and your list first. That said, BIMI is heading toward becoming an industry norm, so it’s smart to budget for it down the road.
3. Clean up what’s inside the email
Once your list and your records are solid, the content itself can still get you filtered. Spam systems read your email, and a few common things trip them up:
Avoid spammy keywords. These are promotional trigger words in the subject line or body, like free, credit, refund, offers, acceptance, and act now; they all raise your spam score. You don’t have to strip every sales word from existence, but go lighter than feels natural. If you have a lot to promote, send a short email that points people to a landing page where the full offers live. It’s also worth dropping emojis from subject lines, since they can trip filters too. A free spam-word checker is an easy way to catch the worst offenders before you send.
Keep your links in check. Too many links look spammy, so aim for fewer than twelve per email. And long URLs are a problem of their own. Some filters penalize links over 120 characters, and image URLs are a sneaky culprit here. When an image sits several folders deep, its address balloons. Move images closer to the root of your hosting and keep file names short, and those URLs shrink fast.
Fix broken characters. Odd symbols that show up from bad encoding or copy-pasting out of Word or Google Docs make an email look sloppy and suspicious to filters. Give your final copy a quick scan for them.
Go easy on the HTML. Drag-and-drop email builders (and MJML exports) generate far more code than a hand-built email needs. They pack in nested tables, wrapper elements, and repeated inline styles. All that bloat makes your email heavier and can push you past Gmail’s 102 KB limit, at which point Gmail clips your message and hides part of it. To fix this, export the HTML from your template, paste it into an AI tool like Claude, Perplexity, or ChatGPT, and ask it to clean up the structure. You’ll get a lighter, tidier version in seconds.
One more content-adjacent tip: rethink open tracking. A few EU markets, including Italy and France, are moving toward requiring explicit consent to track email opens. Click-through rate is a more reliable signal of interest anyway, so leaning on CTR over opens is a reasonable call.
4. Send like a person, not a firehose
How you send matters as much as what you send. Inbox providers are pattern-watchers, and erratic behavior makes them nervous.
With that said, it’s important to warm up anything new: A new domain, mailbox, or IP has no reputation yet, so don’t come out of the gate with a huge blast. Start with small volumes to your most engaged contacts, then increase slowly and steadily. High early engagement from people who genuinely want your emails builds your reputation quickly, which lets you safely reach less-engaged contacts later. The same caution applies after a long pause. Ramping back up too fast reads as suspicious.
Then, be sure to keep your daily volume steady. Say you’re aiming for around 500,000 emails a week. Sending 300,000 on Monday and 50,000 on Tuesday sends a jumpy, unpredictable signal. Spreading it evenly, roughly 100,000 a day, looks far more stable, and that steadiness correlates directly with a healthier sender score. This one is genuinely hard to pull off in practice, since it fights against campaign calendars and team workflows, but it’s worth aiming for even if you only get partway there.
5. Watch the signals that matter
Segment your audience by engagement and send accordingly. Group your contacts by how recently and how often they’ve interacted, and stop emailing the cold ones.
Mailing inactive people drags down your open rates and raises your spam risk, and that hurts everyone else on your list too. Set realistic expectations while you’re at it: one recent benchmark put average read rates around 23%, so plenty of unopened mail is normal even on a healthy list. Aim for a stable, predictable cadence rather than going quiet for weeks and then flooding inboxes.
And know your bounces. A hard bounce is permanent, usually a bad or mistyped address (someone entering “hotmal” instead of “hotmail,” say), and those should come off your list right away. A soft bounce is temporary, like a full mailbox, and it’s fine until it keeps happening. The ones to really watch are spam complaints, the reports generated when someone hits “report spam.” A rising complaint rate is a loud signal that something needs attention.
Next, make sure you’re keeping tabs on click-through rate, bounce rate, and spam complaints, and pause underperforming campaigns quickly instead of letting them run. Watch your sender score and check that your domain and sending IP aren’t showing up on blacklists. If you set up DMARC reporting earlier, those reports are your early-warning system.
Once your email is ready, always test before you send (obvious at this point, but still important!). Run your email through inbox placement testing to see where it actually lands across providers before it goes to your full list. Gmail tends to be the strictest, so if you’re reaching the inbox there, you’re usually in good shape elsewhere.
And while you’re cleaning things up, positive engagement signals help. Warming activity that generates real opens and clicks can offset the drag from unengaged contacts during the transition, giving your reputation some breathing room while your list gets healthier.
Where to start
If you’re staring at all of this wondering what to touch first, here’s a preliminary checklist you can follow (Ideally, have a tool like Email on Acid or Litmus to help you through this process):
- Align email subject lines with body copy
- Add a preheader
- Verify sender options (Make sure you’re sending from a valid email address and domain that’s set up against SPF and DMARC)
- Confirm that all links are functional and correctly redirectedÂ
- Keep HTML under 100kb
- Keep image weight under 150kb
- Make sure everything is mobile responsive
- Make sure all records are marketableÂ
- Remove all bounces from your list.
None of this is quick, and you won’t fix it all in a week. But deliverability rewards steady, consistent effort. If you’d like a hand auditing your setup or working through any of these steps, that’s exactly the kind of thing we do. Reach out to us here!