Is it possible to secure the mail server mail.example.com with Let’s Encrypt SSL certificate when the A record for example.com is pointing to another server?

Question

Is it possible to secure the mail server mail.example.com with Let’s Encrypt SSL certificate when the A record for example.com is pointing to another server?

Answer

Currently, such a functionality is not implemented in Plesk yet.
Consider voting for this feature on the UserVoice portal. The top-ranked suggestions are likely to be included in the next versions of Plesk.

Alternatively, issue a certificate from another authority and secure mail using it:
How to install an SSL certificate for a domain in Plesk (Let’s Encrypt / other certificate authorities)