This error you can get when the mail server can not handle TLS 1.2 or higher. Could it be that the mail server you are trying to connect to can only use TLS 1.1?
This error you get when a secure connection is being tried to set up but the client and the server can not find an allowed protocol or cypher to communicate with each other.
Regards,
Ronald
The problem looks like it’s secure certificate on the mail server related, so this is the area I would look at.
Do you control the mail server? If you do, has it been updated recently, potentially with a new certificate (self signed?)