Why does Gmail prevent me from sending emails via SendGrid? I've always done this and recently I'm being totally blocked.
The message I receive is as follows:
The gmail.com server informed us that this message bounced. To protect your deliverability, we won't send to this address anymore.
If you want to send to this address, you may remove it from the Bounces suppression group.
Full response from the gmail.com server:
553 5.1.2 The sender address
<bounces+6452016-d6d6-******=gmail.com@ 5.1.2 _mail.***.**>is not a valid RFC-5321 address. z1-v6si718011qtz.4 - gsmtp
If anyone has any clue how to solve this, I'll be grateful.
TL; DR: this was probably a bug in Sendgrid's platform, which they appear to have fixed.
We also had the same issue, and raised a ticket with Sendgrid about it a few weeks ago.
After several rounds of back-and-forth we were sure that the issue was on their side - their system was adding spaces to the return-path which recipient servers like Google then rejected.
bounces+6452016-d6d6-******=gmail.com@ 5.1.2 _mail.***.**
^ invalid space here
In our case this only happened when there was more than one recipient specified for the email.
The Sendgrid support team were very helpful in digging into the issue, and they came back to us a few days ago to say that they have pushed a fix on their side. This seems to have resolved the issue for us and we're no longer seeing messages rejected for invalid return addresses.