I setup ssl for server.domain.com hostname for ispconfig itself and created a vhost with hostname mail.domain.com and also set ssl for that hostname for mail ssl. And in postfix I pointed to this ssl path: Code: # TLS parameters smtpd_tls_cert_file = /etc/letsencrypt/live/mail.domain.com/fullchain.pem smtpd_tls_key_file = /etc/letsencrypt/live/mail.domain.com/privkey.pem myhostname = mail.domain.com And was able to confirm tls https://ssl-tools.net/mailservers/ here. Problem is Thunderbird setup runs fine on first mail account setup (can send and recieve mails with ssl enabled ports 465 - 995) but if I restart Thunderbird, it ask for ssl exception popup and there it points ssl is pointing to server.domain.com NOT mail.domain.com Do I really have to use server.domain.com for incoming and outgoing servers ? When thunderbird show popup for securtiy alert, there I see mail.domain.com:995 and if I remove :995 it can validate ssl fine. I setup mail on my myEmail app on mobile device. And it works fine. It could be related to Thunderbird?