Recently, Dovecot was automatically updated on one of the servers with cPanel, and the PHP self-recording system stopped importing letters, that is, it could not connect to the mail server, in the log file /var/log/maillog I discovered the following:
dovecot: pop3-login: Disconnected (no auth attempts in 0 secs): user=<>, rip=X, lip=X, TLS handshaking: SSL_accept() failed: error:140760FC:SSL routines:SSL23_GET_CLIENT_HELLO:unknown protocol,session=<…>
Then I looked at the configuration file /etc/dovecot/dovecot.conf and compared it with the file in the backup, as it turned out, the line changed after the update (TLSv1 was specified before the update):
ssl_min_protocol = TLSv1.2
To indicate TLSv1, I opened the WHM panel – “Service Configuration” – “Mail Server Configuration”, where “SSL Minimum Protocol” chose “TLSv1” and clicked “Save Changes”, then in /etc/dovecot/dovecot.conf also indicated tlsv1.
After this error did not appear.
I note that the error may also occur if the connection is made without SSL and the configuration indicates:
disable_plaintext_auth = yes
ssl = required