- Plesk for Linux
- Plesk for Windows
How to secure mail the server
mail.example.com with Let's Encrypt SSL certificate when the A record for
example.com is pointing to another server?
This feature is yet to be implemented in Plesk.
You may vote for this feature on the UserVoice portal. The top-ranked suggestions are likely to be included in the next versions of Plesk.
As alternative solution, 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)