I think more of the problems are your infrastructure. You have email configured for ourlimm.dev but then your SMTP server has this information:
220-server1.ourlimm.training ESMTP Exim 4.94.2 #2 Wed, 05 May 2021 12:52:06 -0500
220-We do not authorize the use of this system to transport unsolicited,
220 and/or bulk e-mail.
as you can see here, you now have ourlimm.training as a domain name for your mail server. Try changing ourlimm.dev to ourlimm.training for your SMTP settings. As there is zero consistency between any of your domains for email delivery to be successful.
Whatever banners are passed via the configuration of SMTP ports 25, 587 are going to come from that training domain. I don’t believe the Gitlab certificates are the problem, since any certificates under Gitlab with LetsEncrypt will match the domain name of the gitlab server itself. Of course assuming you configured external_url to use HTTPS.
All MX records for your domains should also match the SMTP name of your server. Otherwise you can expect mail delivery problems. This also applies for PTR records, because even checking that, they don’t match the name of your server either:
server1.ourlimm.training. 14400 IN A 188.8.131.52
dig -x 184.108.40.206
220.127.116.11.in-addr.arpa. 86400 IN PTR server1.auth-loginweb.com.