What’s the first step when open rates drop suddenly?

Your open rates just fell off a cliff and your first instinct is to start changing things. Resist that. Changing multiple things at once is how you lose track of what actually fixed it (or made it worse).

Here's the order to work through it.

Step 1: Check your authentication

Before anything else, verify your SPF, DKIM, and DMARC records are passing. A misconfigured or broken authentication record can tank your sender reputation almost overnight. Check your DNS for any recent changes, even ones that seem unrelated to email. Hosting migrations, domain transfers, or IT "routine maintenance" can silently break your auth setup.

Step 2: Open postmaster tools

Gmail Postmaster Tools will show you your domain reputation and spam rate trends directly from Google's perspective. For Microsoft, check SNDS (Smart Network Data Services) to see how Outlook is reading your traffic. These tools tell you whether you're actually hitting inboxes or being filtered, which is a very different problem to diagnose than a broken authentication record.

Step 3: Run a blocklist check

Check whether your sending domain or IP is listed on any major blocklists. Spamhaus is the one that matters most. A fresh listing can explain a sudden drop across multiple providers at once. You can run a quick check with our free blocklist checker if you want a fast answer.

Step 4: Narrow the scope

Ask yourself three questions. Is the drop happening at all providers or just one? Is it affecting all your campaigns or just certain ones? Is it across your whole list or a specific segment? Narrowing the scope is how you separate a technical problem from a reputation problem. A provider-specific drop almost always points to reputation. A universal drop points to authentication or a blocklist.

Step 5: Look back 48 to 72 hours

What changed right before the drop? New IP or domain? New content template? A campaign with unusually high complaint rates? A list import from a new source? Sudden drops almost always have a trigger. Your job in this step is to find it. (And yes, sometimes it's something that seemed totally innocent at the time.)

If you've checked all five and you're still not sure what you're looking at, that's not a bad time to talk to a human before you start making changes blind.