On June 6th Google made a major change to Gmail’s spam filters. It will be evident in an old, familiar response:
“Our system has detected that this message is likely unsolicited mail. To reduce the amount of spam sent to Gmail, this message has been blocked. Please visit Why has Gmail blocked my messages? - Gmail Help for more information.”
However, you’ll notice it much more frequently than before. Current trends suggest that a broken SPF record may be the easiest way to trigger this, but certainly not the only one. A perfectly valid and legitimate URL in the email body could do it just as well. Here’s a look at some numbers so you can see it happen in real time, all based on UTC:
1346 (Day still going and yesterday I blocked domains with no SPF record)
Speaking with other mail operators, this appears to be a shared experience across the board showing that it is in fact a change at Gmail, not a change in reputation at any particular mail service.
If you are having trouble sending mail to Gmail from your domain, use mail-tester.com and aim for at least a score of 8, a score of 10 would obviously be better. Good luck out there!