I noticed DirectAdmin supports TLS SNI for imap/smtp with Let's Encrypt on their latest release. I've test it and it works really nice. But I'm more of a ISPconfig person then DirectAdmin. I'm curious: is it already possible to support TLS SNI for Postfix/Dovecot with Let's Encrypt on ISPconfig3? If not: are their any plans to implement this? The end result is you can host multiple domains on 1 IP-address and not only do https: for every domain, but also present a valid Let's Encrypt-certificate for mail-connections (pop/imap & smtp). Running Ubuntu 16.04 (Xenial) and ISPConfig Version: 3.1.8p1. Thanks!
Not quite sure how they got postfix to support SNI, maybe they patched it or they use a different SMTP server. From Postfix TLS page http://www.postfix.org/TLS_README.html: and unless postfiux supports SNI, we can't support SNI in ISPConfig for Postfix.
I'm sorry, I should have mentioned DirectAdmin is using Exim. My bad. https://forum.directadmin.com/showthread.php?t=53967 But it's logical if Postfix doesn't support it, it's hard to implement ISPconfig. :-( Luckily it's not a crucial feature but it would be neat if it worked.
In Version 3.4 postfix added SNI support, so adding SNI to deovecot and postfix would be possible by now ...