How to troubleshoot a problem that does not receive notifications in the mail?

Question

SMTP

There is a self-managed gitlab
v. 13.12.4
Push alerts are configured, I'll attach the screenshot below.

And below are valid mailboxes, the letter does not arrive in any way (in projects this alert is "attached" everywhere) where to dig?
PS after the user was deleted, some data was rubbed off, after my arrival, the past was deleted and the alerts disappeared.
Thank you in advance for your response.

Answer 1

Colleagues, I understood a little.
But now the next problem:
I got an interesting case. They transferred the server to another hoster, respectively, received a different IP address, sends letters to mail.ru normally (by type: new merge, new commit, new push)
But does not want to gmail.
Postfix logs say something like this:

The IP you're using to send mail is not authorized to 550-5.7.1 send email directly to our servers.

Obviously went to spamhaus. ( https://www.spamhaus.org/ ) Yes, it is clear that the IP address is blocked on some of the services, the question is different, they ask to write a letter to them from this mailbox, how to do this?
Through cli, is it possible to go to the site and write? oh
PS MB I don’t really understand, but the mailbox looks like this:
[email protected]