There are a bunch of posts in the community about sending e-mail via gmail - maybe one of those will help? If you find the answer in them, be sure to post and mark it here since some of those are missing the “Solution”. If you don’t find a solution, let me know what you tried and we can troubleshoot more.
I transferred your settings onto my system and spent the morning coffee playing with it. I was getting the same error and realized it was likely because I had 2FA set up on my gmail account. I went in and generated an app password for gmail which got me through the error only to be blocked by my own firewall rule that only allows e-mail via authorized systems… more change than I am willing to test out. Since you have other systems happily accessing Gmail, this is likely not the solution, but maybe it will jostle some area you have where the fix is?
Thanks for taking time to investigate, much appreciated. though I was going mad. yeah we have done everything from the gmail side, less secure apps enabled, as well as 2fa disabled for this email.
Will prob have to think about what notification method we could use, slack, opsgenie,etc.
or a postfix server
A big facepalm from this end . The issue wasn’t anything to do with Graylog, but a simple password typo.
correcting it worked like a charm… And a big thank you, you last comment, and prompt, and timely response. made me re-check my entire config
Out of courtesy have posted the working config - also if your using gsuite as your IDP, you need to whitelist the IP of the server, ours was in AWS, so Nat Gateway Public IP.
Apps → Google Workspace - > Settings for Gmail → Routing
under SMTP relay service
edit - and add your IP address