The first version of SNI support for Mail is available in Plesk Obsidian: https://docs.plesk.com/release-notes/obsidian/change-log/#18-rc10
You need MailEnable 10.20+ (for Windows) or Postfix 3.4+ and Dovecot (for Linux) to test it.
There are cases when it doesn’t work (e.g., if you connect to mail.domain.com it will not work, please use domain.com in connection settings of your mail client) that’s why we don’t mark it as “available”. We plan to fix these issues soon.
— rkMario Voigt commented
I was able to solve this problem by using a multidomain wildcard cert. But native SNI would be cooler than that