Deliverability problems are sneaky. Nothing breaks. Revenue per send slides a little each month, the team blames the creative, and sends more to make up the difference, which makes it worse. By the time someone checks, a large share of the list has been reading you in the spam folder for a quarter.

The rules changed in 2024

Starting February 1, 2024, Google required anyone sending more than 5,000 messages a day to Gmail addresses to meet a set of rules Published. Yahoo announced matching requirements. Once you cross the threshold, Google treats you as a bulk sender permanently.

• Authenticate your domain with SPF and DKIM, and publish a DMARC policy. At minimum, DMARC can be set to monitor only.
• Offer one-click unsubscribe in the message header, plus a visible unsubscribe link, and honor unsubscribes within two days.
• Keep the spam complaint rate low. Google asks senders to stay below 0.10% and to avoid ever reaching 0.30%. Yahoo’s line is 0.3%.

Most email platforms handle the header and the link. The domain records are yours. So is the complaint rate, and it’s the one that moves. Set up Google Postmaster Tools on your sending domain today; it’s free and it’s the only direct view you get of how Gmail sees you.

Your spam complaint rate is the most important email number most teams have never looked at.

Opens stopped meaning anything in 2021

In September 2021 Apple shipped Mail Privacy Protection with iOS 15. When it’s on, Apple Mail downloads an email’s images in the background, whether or not the person reads it Published. Opens from those readers are recorded automatically. Open rates rose across the industry as people updated their phones, and they’ve been unreliable ever since.

This matters in three places. Don’t judge subject lines on open rate alone. Don’t define “engaged” by opens only; include clicks, site visits and purchases. And don’t let a healthy-looking open rate reassure you about deliverability. An account can show strong opens and a collapsing click rate at the same time, and the click rate is the one telling the truth.

What a deliverability problem looks like

It rarely looks like a problem. Open rates hold, because of the Apple change. Click rate drifts down a little each month. Revenue per campaign falls, and the team decides the creative is tired. In Postmaster Tools, domain reputation slips from high to medium, and the spam rate line touches 0.1% on the days you mail your widest segment. If you see that pattern, the fix isn’t new creative. It’s narrowing who you send to for a few weeks, letting the engaged readers rebuild your reputation, and widening again slowly.

The habits that keep you out of spam

• Send to people who read. Build campaign audiences from engagement windows: people active in the last 30, 60 or 90 days, depending on how often you send. Send to the less engaged less often.
• Sunset the silent. Subscribers with no engagement for a long stretch get a short last-chance series, then are suppressed. It feels like throwing away list. It’s protecting the inbox for everyone else.
• Send from a real brand address, from your own authenticated domain, with a name people recognize. From my work: I’ve seen a cart recovery flow sent from a staff member’s personal address, with an open rate a fraction of the account’s other flows. Changing the sender was the whole fix.
• Warm up anything new. A new domain, a new platform or a big list you haven’t mailed in months goes to your most engaged readers first, then widens over weeks.
• Make unsubscribing easy. A person who can’t find the link clicks “report spam” instead, and that costs you far more than a lost subscriber.

Do this

• Check SPF, DKIM and DMARC today, set up Postmaster Tools, and add spam complaint rate to the weekly report. If it’s above 0.10%, stop sending to your least engaged segment until it’s back down.