Email deliverability is not mysterious. It is just boring hygiene people ignore until their revenue gets wrecked.

I get asked to audit email lists all the time, usually after someone notices opens falling off a cliff and assumes the copy is the problem. Sometimes the copy is bad, sure. Most of the time, the list, authentication, sending pattern, or some hidden tracking junk is quietly poisoning the account.

Over the last few years, I have worked with over a billion sends, seen open rates in the mid-60s, and helped generate hundreds of millions in revenue outside the normal funnel. I have also sat with ESP teams to fix platform-level deliverability issues, so this is not theory for me. It is the exact checklist I use when I want to find the problem fast.

The audit takes under 5 minutes once you have the basics:

Sending domain, like name@yourdomain.com
Sending IP, though most people are on shared IPs
Google Postmaster access from postmaster.google.com
Access to the ESP, because the final part only makes sense inside the platform

I do not start with open rate. Open rate is the symptom. I want to know what Gmail sees before anyone starts blaming the subject line.

I start at mxtoolbox.com. The domain goes into the search box, then I pull DNS records and check SPF, DKIM, and DMARC until they are clean. Not mostly clean. Clean. DMARC set to none is not a good look if you mail daily anymore. For daily sending, I want quarantine or reject.

If the records look right but there is still an SPF warning, the usual culprit is too many SPF records. Flatten them. Tools like autospf.com are cheap and do the job. The point is to combine the mess into one clean record so mailbox providers are not tripping over conflicting signals.

Then I stay in mxtoolbox and check blacklist status. If the domain or IP is listed, I go through the removal process. A lot of these are automatic. UCEProtect is the annoying one because the level matters. Level 1 usually means the domain did something wrong. Level 2 usually means the IP block did something wrong. Level 3 usually means the server block is the issue.

Level 1 means I look for bad acquisition. Scraped leads, bots hitting forms, fake signups, anything that should never have been mailed. Level 2 means figuring out whether the sender caused it or inherited it from neighbors on the IP block. If it is inherited, the ESP needs to move the sender to a cleaner block. Level 3 is the hardest because the sender has to push the ESP to talk to the server owner and move the IP or remove the bad account. ESPs often say there is nothing they can do. There is usually something they can do. It is just a pain, and they fight it because it takes effort.

After that, I go into Google Postmaster and check Authentication first. If it is not 100%, fix it. A lot of deliverability problems are hiding right there. If a tab is missing, I do not guess. I fix access first because Postmaster data is the closest public view into how Google is treating the domain.

Then I look through every tab: Spam Rate, IP Reputation, Domain Reputation, Feedback Loop, Authentication, Encryption, and Delivery Errors.

Spam Rate needs to be 0.1% or lower. If it is around 0.2%, there is a real spam problem. One practical move that helps is putting the unsubscribe link near the top of emails at least once a week. Make it easy for people to leave instead of making them hunt for the exit.

IP Reputation is often outside your control on shared infrastructure, but if you have a dedicated IP, I want to know whether it is High, Medium, Low, or Bad. Domain Reputation is different. That one is much more in your control because it follows your domain, your content, your list quality, and your sending behavior.

Feedback Loop is usually an indicator of misconfiguration or a technical error, not the main crime. Authentication should be 100%. Encryption should also be 100%. If encryption is failing, something technical is broken somewhere in the setup.

Delivery Errors is a big one. If it is not 0%, I treat it as a fail. Either the sender is trying to mail addresses that cannot be mailed, or the setup is misconfigured. Both are bad signals.

Once that stack is clean, I move into the ESP and look at two things: consistency and volume.

Consistency means the account sends in a pattern mailbox providers can understand. Daily, twice daily, every other day, every Monday, once per month, whatever. The pattern has to be real. Saying I send every Tuesday is consistent. Saying I send whenever there is a promo is not consistent.

Volume means the daily average stays stable. It is not about every single send being the same size. It is about the account not swinging from tiny sends to huge blasts with no warning.

For example, on one list I managed, the daily average was around 500,000 sends. That might be spread across 30 or 40 emails. One send might go to 500 people and another to 50,000 people. The individual sends varied, but the daily average stayed predictable. That is the number I care about.

If someone sends once per week, I check whether the weekly average is stable. If they send once per month, I check the monthly average. Same for yearly patterns. This is one of the biggest reasons accounts with perfect SPF, DKIM, DMARC, and Postmaster data still have inboxing problems. The setup is clean, but the sending behavior is chaotic.

Promo volume is not a magic excuse anymore. This is not 2007 on an old ESP account with a stolen list. Email is harder now. If the account has strong reputation, I am comfortable increasing volume by around 10%. I will push closer to 20% only when IP reputation is high, domain reputation is high, the other tabs are clean, and open rate is strong.

Then I check bounce rate. The accounts I have managed that scale safely usually keep bounces far below a tenth of 1%. That means well over 99.9% acceptance. That is not an inboxing number. It is an acceptance number, meaning the receiving system accepted the message.

The rule is simple: if an address soft bounces once, stop mailing it. If it hard bounces once, stop mailing it. No second chance.

The way to execute that is a suppression segment called BOUNCED. Add that segment to every send on the suppression side so those contacts do not receive mail. Do not delete them. Their data is still useful. Just keep them out of active sends.

People always ask what if that address would not bounce again. That is not the point. In a six-month test with well over 100 million sends, the chance of a bounced address not bouncing again on the next attempt was tiny. The upside of retrying it was not worth poisoning the rest of the send.

For every 1,000 bounced addresses, you might recover a few dozen. But you are risking hundreds of good sends and teaching mailbox providers that your list hygiene is sloppy. I would rather kill the bad addresses than let them damage the good ones.

If everything above is clean and open rates are still bad, then the problem is usually the email itself. Either the copy is triggering spam signals, or there is some stupid hidden tracking code, pixel, footer hack, or invisible text messing with the message.

I know this because I have been on enough calls with Gmail, Yahoo, Outlook, and Microsoft teams to hear the same thing from people who actually make decisions there. Their systems are getting better at recognizing cheap deliverability tricks. They have reviewed accounts and shown internal feedback patterns that make it clear: the hacks are not as clever as people think.

Clean copy gets more eyeballs. More eyeballs create more chances for clicks. More clicks create more chances for sales.

The metric people obsess over is CTR, but I care more about total unique clicks and total sales. If I can get 10 times more people seeing the email and CTR drops by 3 times, I am still way ahead. That is why deliverability matters before optimization. You cannot click an email that never lands.

On promo sends, I have seen EPC average around the high double digits. On tighter niche segments, it can be much higher. We have also seen sends with far fewer clicks produce way more sales because the list strategy was better. That is the part most people miss. Deliverability is not just a technical setting. It is a revenue system.

So the short version is this: authenticate properly, keep Postmaster clean, remove blacklist issues, suppress bounces aggressively, send consistently, control volume, and stop using cheap tricks in the email body. The accounts that win are not the ones with the most hacks. They are the ones that make boring, predictable, trustworthy sending look easy.