When trying to connect to a mailbox on a Plesk server using SSL/TLS (POP3S on port 993 or IMAPS on port 465) the connection is not established
The error below can be found in the file
dovecot: pop3-login: Disconnected (no auth attempts in 0 secs): user=<>, rip=XXX.XXX.XXX.XXX, lip=XXX.XXX.XXX.XXX, TLS: SSL_read failed: error:14094412:SSL routines:ssl3_read_bytes:sslv3 alert bad certificate: SSL alert number 42, session=<kdjKIaiqCyC/t2TL>
The SSL certificate securing the mail server at Tools & Settings > SSL/TLS certificates is different from the mailbox that is being configured.
Note: SNI support is not available to the Postfix mail server on Plesk Onyx, more details here.
Upgrade Plesk server from Onyx to Obsidian, since Plesk Obsidian has SNI support.
Note: In case update to Plesk Obsidian is not possible, the domain, in which SSL certificate is protecting mail server in Tools & Settings > SSL/TLS certificates, should be configured as mail server address on the mail client software (Outlook, Thunderbird, etc.).
Secure mail on the domain by using the instructions from the article below:
How to assign a SSL certificate per domain to secure the mail server in Plesk (SNI support)