How to Diagnose and Recover From Deliverability Disasters
Nothing induces panic faster than realizing your emails are suddenly not reaching the inbox. It’s like someone pulled the fire alarm on your day — your blood runs cold, you’re in crisis mode, and you haven’t even had coffee yet.
Whether it’s a subscriber reporting your message in spam, a drop in open rates, or your support team’s Slack channel lighting up like a Christmas tree because confirmation emails aren’t going out, your boss wants answers. Yesterday.
Sound familiar? Good. You’re not alone. But panicking won’t get you back in the inbox.
Which is why today’s lesson isn’t just about putting out fires. It’s about diagnosing what went wrong, cleaning up the mess, and putting safeguards in place so you don’t find yourself here again (and again, and again 😒).
So, let’s get into it.
Step 1: How to Know When You’re In Trouble
Not every dip means disaster. But you don’t wanna wait until you’re seeing massive performance issues to start poking around. The mess will be much harder to clean up by then.
Here are the most common signs that something’s actually wrong:
💌 Performance cliffs
You’ve seen ‘em. Sudden drops in delivery rates, opens, clicks, or conversions. I don’t mean small blips and variations — those are common, even when using similar subject lines, email copy, and segmentation. Here, we’re talkin’ about when one (or several) of your metrics falls off a cliff like that little yodeling mountain climber from the Price is Right. If that happens, and things haven’t bounced back by the time you’re noticing it, you need to get ready for action.
💌 Recipient complaints
Hearing from customers who didn’t receive mail they should’ve, like a password reset email or a purchase confirmation — or telling you they found your mail in their spam folder — suuuuucks. But it’s also a golden lil’ nugget of info you can use to figure out what’s going on. As Al Iverson said just the other day, “you can't fix what you don't know about.”
💌 Compliance flags
Landing on your ESP or internal compliance team’s radar usually means your stats are out of order (e.g. high bounces or spam complaints) or you’re causing problems for sender reputation (e.g. triggering blocklistings, hitting spam traps, or impacting deliverability for other customers).
If they’re flagging an issue, don’t ignore it.
💌 Deliverability alerts
Third-party tools can be used to identify a wide variety of issues related to authentication or engagement, spam trap hits, blocklistings, domain/IP reputation, and more.
Some are free, like Google Postmaster tools. I highly recommend you connect your domain (as long as you’re sending more than a few hundred messages per day to Gmail users) to not only know if you’re compliant with their sender requirements, but also to know what they think about you as a sender. If you see Google Postmaster Tools showing your domain reputation dropping from High to Low — get movin’. You’ve got a real issue on your hands.
Other third-party tools, such as email analytics platforms (like SocketLabs Spotlight and SEINō) and deliverability platforms (like GlockApps, Inbox Monster, Mailmonitor, and Validity) provide a wide set of monitoring tools so you can identify issues more quickly and jump straight to figuring out if they’re a big deal or a little deal.
These are typically reserved for organizations sending high volumes or email, or those who rely heavily on email for revenue generation, but can provide powerful insights to any sender interested in maintaining consistent inbox placement.
Step 2: Find the Root Cause (Not Just the Symptoms)
Most senders jump straight to “fixing” without figuring out what broke in the first place. That’s a mistake… one that will slow your resolution time and potentially cause noise for people who don’t need to get involved (yet, anyway).
Deliverability issues may be a cocktail of causes, so before you fire off your re-engagement campaigns or start rewriting all your copy, stop and ask yourself:
💌When did this start?
Don’t just look at when you noticed the issue… see if you can trace it back to when performance actually started falling off. In some cases, it’s that performance cliff we talked about; in other cases, it’s a slow decline that actually started months ago. Get your goggles out and trace the timeline.
💌Where is it happening?
Are all mailbox providers affected, or just one? Scope matters. It helps you prioritize, but can also give you helpful information about what’s driving your issue.
For example, Gmail is very heavily focused on user engagement, so if your open rates are 2% at Gmail while they’re +30% at other top destinations you send to, you’ve got a spam folder issue. You can now turn your attention toward recipient reactions (spam complaints, opens, clicks, unsubscribes).
But if Microsoft is bouncing everything in sight, you’ll want to look more closely at authentication, blocklists, and IP reputation.
💌What changed upstream?
Sure, it could be your ESP or the mailbox provider themselves having problems delivering your mail, but 9 times out of 10, that call is coming from inside the house. So, take a good look around to see if anything (and I mean anything) may have changed on your side.
Did you:
Launch a new campaign that got a different reaction?
Add a new segment or acquisition source?
Did you change frequency?
Switch platforms or mess with DNS?
Ultimately, you can’t fix what you don’t understand, and even a small change can ripple downstream. Be sure to diagnose your issue before you pull out the duct tape.
Be methodical. Follow wherever the data leads you, and find what stands out as odd… because it’s there, somewhere:
Dig into bounce responses (e.g. “this address does not exist” and “Your email was rejected due to having a domain present in the Spamhaus DBL” have two completely unrelated root causes)
Side-eye elevated spam complaints and unsubscribes as an indication of negative sentiment within your email audience
Compare domain-level performance over the past 30-90 days (delivery rates, opens, clicks, unsubscribes, and complaints)
Check the headers of emails you send — if SPF, DKIM, or DMARC are failing, that could be contributing to the issue. We’ll dig into these more in Step 4.
If you have spam trap feeds or blocklisting monitors, check your recent activity
We’re just scratching the surface here. If this already sounds painful and you’d rather talk it through, hit me up. Sometimes a 20-minute chat beats a 5,000-word rabbit hole (even though I looooove a good deliverability rabbit hole). 💌
Step 3: Your List Is (Probably) the Problem
Most deliverability issues boil down to bad data. In one way or another, it’s the #1 driver of inbox issues. Either you’re sending to people who didn’t ask for it, or you’re sending things they don’t care about. So, check it again (if you haven’t already).
The following may be contributing to your issue…
💌 List growth missteps
Not getting explicit permission at signup. I’m not talking about what legally counts as an opt-in… for example, acquiring a list of “opt-in” addresses from a partner or affiliate. If they’re not aware of the fact that your brand will be emailing them, just don’t do it.
Not clearly setting expectations. They should know exactly what they’re signing up for before they submit their address. And ideally, you follow up with a welcome email that reinforces who you are and why you’re in their inbox. Then you stick to what you promised! If you haven’t defined re-engagement or sunset policies yet, skip ahead to Step 6 — it walks you through how to build them.
Not validating email addresses at the point of entry. Sometimes, even the most legitimate brands pull in trash signups… perhaps because they’re running a sweepstakes that entices people to share disposable email addresses. Or their form isn’t protected with a CAPTCHA (or similar line of defense against bot signups). Quick plug for real-time email verification if you’re collecting a LOT of addresses and delivery rates are often below ~95%.
Sending mail that’s disconnected from what they signed up for. For example, if your last sweepstakes attracted people who only wanted a free iPad, not your content. Keep it relevant to what you’ll be emailing them about, people! Email is about quality, not quantity.
💌 List management flaws
Changing your frequency or volume without warning. Mailbox providers like consistency. When they notice changes in recipient reaction or sending volume, they’re likely to figure you’ve been hacked (and someone else is running amok with your sender reputation), or you’re doing something squirrely (in which case, well, maybe you don’t deserve the inbox anymore).
Sending infrequently (e.g. once every 6 months). This one’s also a red flag for mailbox providers since they don’t have enough recent sending history to know if you’re safe for their users. Not to mention, recipients may forget about you, making them more likely to mark your emails as spam.
Not acting on engagement data. You’ve gotta pay attention to your positive engagement signals (e.g. opens and clicks) and the negative ones (e.g. marking your email as spam or unsubscribing) to ensure you’re only sending to people who actually want to hear from you. Suppressing people who’ve asked to get off the ride isn’t just good for deliverability… it’s also legally required in a lot of parts of the world.
Not having a re-engagement or sunset policy. Want to know what ‘unengaged’ should mean for your brand, or how to build re-engagement flows? That’s coming up in Step 6.
Step 4: Act Strategically, Not Desperately
Once you’ve identified what changed and have a hypothesis about what’s hurting your deliverability, it’s time to act. But please don’t panic. This is not the moment to start throwing spaghetti at the wall — or to change five things at once and hope for the best.
Here’s how to proceed without making the situation worse.
💌 Suppress the Right People
Remove unengaged recipients from your active mailings. This can be super helpful in the short-term when you’re seeing signs of reputation trouble because mailbox providers will see a higher percentage of their users engaging positively with what you send.
That doesn’t mean applying some generic 30-, 60-, or 90-day rule. I’m not gonna tell you what your definition of "unengaged" should be, because it depends entirely on:
Your send volume and frequency
Your audience’s lifecycle and buying cycle
Your acquisition sources
Your segmentation strategy
The signals you actually have available (and how trustworthy they are)
How aggressively you’ll likely need to pull back and how quickly you start to see improvement is dependent on how aggressive your sending practices have been until now.
💌 Slow Your Roll
If you’ve been mailing everyone all the time, stop. Sending more won’t fix a disengaged list, and if you’re trying to push your way back into people’s faces (and inboxes) while there’s a problem, you’ll only make matters worse.
Let your most recently active and positively engaged folks carry the weight while you stabilize. If you’re running a high-volume program, consider throttling or pausing campaigns temporarily while you monitor.
And when things do start to stabilize, resist the urge to go back to business as usual. It burned you last time, it’ll eventually burn you again. Instead, use this moment to pause and re-assess how often you should really be sending to various segments on your list. Do you really need to blast that recycled webinar invite to your full database? No, didn’t think so.
💌 Fix Authentication Gaps
If you haven’t already, now’s the time to dig into your authentication setup. If anything’s missing, misconfigured, or recently changed, fix it. Authentication won’t solve a poor sending strategy, but failing authentication will absolutely get you flagged.
A few ways you can approach it:
Do a DNS lookup to see if your records are still published (e.g. via MX Toolbox)
View the email headers of the email/campaign having issues: do you see a “pass” or “fail” result for your SPF, DKIM, and DMARC? Quick tip: add your own email address to the emails you’re sending so you can view the headers anytime you want vs having to try to replicate the issue after the fact.
Use Word to the Wise’s AboutMy.Email tool to check your authentication status, as well as if your email is fully compliant with mailbox provider requirements. Note: you’ll need to send an email from your actual production environment to get an accurate picture of your status.
When in doubt, check with your ESP’s support team. They know how you should be setup to send successfully through your platform and can walk you through it.
💌 Don’t Panic-Tweak Everything
If you change five things at once, you won’t know what worked.
Start with suppressing those less-than-stellar addresses. Monitor mailbox-level performance (especially Gmail and Microsoft), and don’t change your frequency or creative unless you have a clear reason to do so.
How long it takes to see improvement depends on the severity of the problem, but taking swift action and implementing changes to fix the root cause will significantly speed up the recovery process. Generally speaking, most senders tend to see delivery improve within a few days to a few weeks.
💌 Watch the Right Metrics
Check daily. By mailbox provider. Over time. Look at:
Trends in opens - while this metric is nowhere near as accurate as we want it to be, they’re still great for deliverability if you follow the trends over time because mail that goes to the spam folder doesn’t trigger an open event. For example, you would clearly be able to see there’s an inbox placement issue with Microsoft if your open rate is 6% whereas it’s 30-40% everywhere else. That’s information you can use.
Complaint rates (mailbox providers recommend you keep them under 0.1%) - spam complaints are super damaging to your sender reputation, so if you see an increase above 0.03% — even if it’s just a one-time thing — dig into the content, the segmentation, and the list source to be sure everything is in order. Conversely, if you see that your complaint rate is consistently at 0.00%, it’s possible you’re going to the spam / junk folder (where people can’t complain / mark you as spam). Referring back to that last bullet point… if you see a low open rate paired with a non-existent complaint rate, there’s a good chance your mail isn’t reaching the inbox.
Bounce codes (especially blocks and policy-based bounces) - a few email pals and I wrote a blog all about bounces, and it shares a lot of examples to illustrate how reviewing bounce classifications and responses can be helpful.
If you use inbox placement / deliverability monitoring tools, don’t treat them as gospel. Most of them are heavily reliant on seed testing (i.e. sending to test addresses automagically managed by vendors instead of real people’s inboxes), and mailbox providers have told me they can very easily tell these apart from human-managed addresses, so you’re oftentimes not getting an accurate reflection of where your mail is actually landing. Use them for directional insight only.
💌 Involve the Right People (Your ESP, Then the Postmaster)
Start with your ESP. Open a ticket. Tell them what’s going on. Ask if they can help you confirm whether it’s just you or a broader issue. They’ve likely seen your issue before and can escalate to the mailbox provider if needed.
Postmaster escalation should only happen once you’ve resolved the root issue — and your ESP agrees it’s time to pull that lever (or they’ve started ignoring you).
A few tips for making the process less painful for everyone involved:
Be prepared. Have dates, symptoms, and context ready to share about what your general practices and reason for sending mail are. And if you’ve made changes to address the issue, tell them that, too! Don’t make them guess — asking follow-up questions takes time, which hurts you more than it hurts them.
Be honest. If you made a risky move — new segments, a sketchy list, or a one-time blast to everyone who’s ever looked at your site — tell them. They can’t help if they don’t know.
Be reasonable. If they present evidence that the issue is in fact on you to fix, own it. And fix it quickly! It’s only going to waste time (and dig your hole deeper) if you try bargaining with them.
Be kind. Even in this age of AI-everything, the majority of interactions you have with your ESP will be with humans. Busy ones who are typically underappreciated and probably dealing with 20 other senders who think their problem is the most urgent thing on Earth. A clear and respectful message will get you better support… and a few karma points for being nice. 💌
Step 5: Debrief & Deliverability Post-Mortem
That’s right… you’ve solved your issue, but you’re not done yet! Because you need to do more than just whack that mole, unless you want it to pop back up again.
So learn from what went wrong. Accept why it happened, and if it was caused by something(s) about your email program that needs improvement, consider how you can take one step toward being a better sender (even if a baby step is all your org will allow… for now).
A few ways to do this…
Document the timeline: What broke? How did you find it? What did you fix?
Build (or revise) your failover plan: Whether that’s better segmentation, a secondary ESP, or a clearer escalation path when something goes wrong, strategize what you can do now to avoid similar issues in the future.
Re-assess your strategy: Know what’s working, what’s not, and when it’s time to let go of inactive addresses.
Train your team: Make sure everyone from marketing to product and compliance understands what can break deliverability… and how to avoid it! Understand that you’ll likely be seen as a “no” person or compliance cop, and prioritize what’s in it for them vs sharing all of the things. Need-to-know basis here, folks. What’s the carrot that’s gonna get those rascally rabbits to play by email’s rules?
Step 6: Fix the Structural Issues
Once you’ve reflected and documented, it’s time for a deeper clean. These are the changes that keep you from winding up here again.
💌 Define Re-Engagement and Sunset Policies
I’m not gonna give a blanket recommendation like “target 90 day openers” because what counts as “unengaged” depends on your business model and goals with email, your content, your frequency, the way you collect addresses… all of it. Even the length of your conversion cycles matters (e.g. fast fashion vs car sales).
If you don’t have a written re-engagement and sunset policy, start there. Figure out what counts as “engaged” and “unengaged” for your brand, cut the slackers, then get back to focusing on your engaged audience!
Be sure to define:
When a contact moves into a re-engagement flow (and what that flow looks like)
How long they stay there
What happens if they come back — ideally, don’t just throw them back into the “active” segment they were ignoring to begin with! Stick with some closer to what worked during your re-engagement campaign.
What gets them suppressed or removed entirely
Base this on meaningful signals (ideally clicks and conversions), not just open activity.
💌 Segment Like You Mean It
There’s no award for "most emails sent."
The actual point of sending all those emails is to connect with your readers. To build a relationship. And in most cases, to eventually turn them into a loyal customer.
So, if your segmentation strategy still includes “anyone who downloaded that whitepaper once in 2021,” and “people we never actually met at the trade show but emailed anyway”, it’s time to clean house. Prioritize recent, meaningful activity — particularly clicks and replies.
One way to do this is to segment based on behavior, not just demographics.
What someone does matters more than what they say in a preference center. Pay attention to how they engage — what content they click on, what products they browse, how often they open or reply.
You’ll get better results (and fewer unsubscribes) when you align messaging with what people have actually shown interest in, not just what they said they wanted once upon a time.
💌 Revisit Expectations
Look at where your email addresses are coming from. What was the promise at sign-up? Did they opt into a high-frequency newsletter — or just grab a gated asset?
Your content and cadence should match what they expected (and what their actions are telling you they like and don’t like), not what’s easiest for your marketing calendar.
I’m admittedly not following my own advice on this one, since my weekly newsletter sometimes comes out once a month, but that’s life when you’re writing a newsletter about work stuff in your free time. Do the best you can, and try not to let it stress you out (I say to myself…). ¯\_(ツ)_/¯
💌 Fix the Basics to Optimize Engagement
Content itself is not usually the reason for a deliverability issue, but the way humans react to said content is.
Avoid image-only emails - always include live text so the email still functions for people who have automatic image-loading disabled.
Make sure emails are mobile-friendly and easy to scan.
Make sure your subject lines match your content.
Include an unsubscribe link that’s easy to find and actually works.
These little details make all the difference between “trusted sender” and “probable spam.”
💌 Build for the Long Haul
You’re not just trying to dig yourself out of a hole… we already played that game, remember? Now you’re onto building a program that won’t need another emergency reset in six months.
So, put systems in place to:
Monitor engagement and deliverability trends (at least monthly).
Document policy decisions so they’re not lost in that meeting where everybody heard something different and nobody took notes.
Run a light audit any time you change something major (IP, domain, acquisition source, ESP, etc.)
Activate a contingency plan (with an internal escalation path outlined) so you’re ready if something does go wrong.
Step 7: Stay Ready So You Don’t Have to Get Ready
Deliverability isn’t something you fix once and forget. It’s a relationship—between your brand, your audience, and the inbox providers trying to protect them.
Want to avoid another panicked Slack thread asking if anyone else’s open rate just tanked? Build better habits now:
Maintain clean, permission-based lists
Set and reinforce expectations early
Suppress disinterest before it becomes damage
Monitor opens, complaints, and bounce codes by provider — they’re your early warning signs
Revisit your strategy quarterly (not just when it breaks)
Do this, and your next dip might not be a disaster. It might be a blip. Or better yet, something you catch—and fix—before anyone else notices.
You’re skipping to the end (again 🙄)? FINE.
Here’s your TLDR…
Don’t just survive a deliverability crisis. Learn from it. Fix what broke. Then build a program that won’t buckle under pressure next time.
Deliverability issues can be scary, but they’re almost always fixable. So, wake up. Pay attention. And replace panic with a plan for Investigation, documentation, and action.
Save yourself time by checking all your bases and diagnosing the root cause before you start “fixing” things or begging for re-entry back into the inbox.
Remember that most problems come down to data, strategy, or recipient behavior (not some mysterious filter voodoo), so keep your lists clean and align your content with audience behavior.
Lean on your ESP. They genuinely care about your success (and closing your ticket ASAP!), so help them help you by sharing facts and context to speed the process.
Review the tapes and prep for next time. Don’t just live through the past. Learn from it! Then adjust accordingly. 💌
Prevention beats cure. Building observability, resilience, and responsiveness into your email program saves you time, money, and stress down the line.
If this sounds like a lot, it is. But in the long run, tackling your issues at the root is a lot better than playing whack-a-mole with your email program until the end of time. If you want help from someone who lives and breathes this stuff (and doesn’t panic at the first blocked message), let’s talk.
Want more content like this in your life?
Send It Right is a blog and weekly(ish) newsletter for marketers and email practitioners who want to reach the inboxes (and hearts) of email recipients. Join 1,080+ other email nerds in subscribing to get the next lesson directly in your inbox. 💌
