Messages getting marked as spam when you send from your own domain name using Gmail?

We recently heard from a couple of customers who set up Gmail to “Send mail as” a different email address at their custom domain name many years ago, and who are now having problems sending mail to people who use for their mail service (the messages were wrongly being flagged as spam at Outlook).

If this happens to you, it’s because the way Gmail used to set this up doesn’t interact well with modern email providers. The way they send these messages makes it look like a “spam forgery” to providers like that check for DKIM and SPF.

You can easily solve this by deleting the address in Gmail, then re-adding it. (If you’re one of our customers, the “Using Gmail to send messages” section of this page on our website shows the settings to use at Gmail.) Google will then set it up in a better way that works with modern email providers.

If you’re interested in the details of the problem: When Gmail first started offering “send mail from another address you own”, they didn’t ask people for the password of their email account. Because they don’t know the email password, they can’t send a message through the normal outgoing server for the email address. Instead, they send it using their servers, but with the “From” address set to the custom domain name. That causes a mismatch between where the messages actually come from and where they’re expected to come from, and the mismatch causes problems when the receiver does certain modern anti-forgery checks.

(Technically speaking, the way Gmail sends these causes problems for SPF alignment checks because the Return-Path envelope sender address doesn’t match the header From address, and causes problems for DKIM checks because the message won’t be DKIM signed. If you’re wondering if you have this problem, you can look at a received email message and see whether the “Return-Path” header is your address instead of the custom domain name address; if the Return-Path is, it’s set up the old way.)

If you re-add the account in Gmail now, they’ll ask for your email password and send your outgoing messages through the expected server, instead of directly through their servers. This avoids the mismatch and solves the problem.