Authentication issue from long distances

[MarcS1975]

I have 2 instances of DMS located in Europe up and running very well. Whenever I connect to DMS (Imap and smtp incl TLS) from far away, i.e. 7,000-10,000 miles away I get locked out by fail2ban. When connecting from closer, say anywhere in Europe DMS all works fine.
The connection issues are not due to the local infrastructure as they are top notch and often better than in Europe. However, of course there is increased latency for any internet traffic going such long distances. Any ideas howto fix this. I am also seeing the following error messages:

2025-01-24T04:05:51.330564+00:00 mail dovecot: imap-login: Disconnected: Connection closed: SSL_accept() failed: error:0A000416:SSL routines::sslv3 alert certificate unknown: SSL alert number 46 (no auth attempts in 0 secs): user=<>, rip=Mail-client-IP, lip=172.30.0.2, TLS handshaking: SSL_accept() failed: error:0A000416:SSL routines::sslv3 alert certificate unknown: SSL alert number 46, session=<9m+l12ssVMF2yCIS>
2025-01-24T04:05:54.287554+00:00 mail dovecot: imap-login: Disconnected: Connection closed (no auth attempts in 0 secs): user=<>, rip=185.236.186.237, lip=172.30.0.2, TLS handshaking: Connection closed, session=<V4/S12ssJKi57Lrt>

[casperklein]

I noticed the same when I once was at vacation. The connection speed seemed good at the first look, but obviously it wasn't the whole time. I also got randomly blocked by fail2ban for incomplete login attempts. I don't think, there is much you can do, except to choose a better connection.

Alternatives:

1. disable fail2ban
2. Connect via VPN to your mail server and whitelist that IP address.
3. Or if you have a fixed public IP address, whitelist that. Or maybe whitelist the whole region (geoip).