Using ssl certificate for Postfix and Dovecot in multiple domains.

[apinto]

Welcome to Sentora

For SMTP/IMAP/POP3 (postfix and dovecot protocols) you can only have one SSL Certificate per IP.

Regarding how email works, if you only have one IP (and one server) you should have a single domain for mail exchange, usually this domain is called mx.domain.tld but you can call it whatever you like.

Make sure that your mx.domain.tld is exactly the same IP address as your Reverse DNS domain (usually this is your hostname, panel.domain.tld), if you use CloudFlare DNS make sure mx.domain.tld does not have the orange cloud.

After this, on the OTHER domains you need, just create a subdomain for them like mx.domain2.tld or even mail.domain2.tld (as long as they point to the same IP as your primary mx server).

The ONLY single drawback is that the client needs to accept the security certificate on the FIRST time they connect, all the emails are sent correctly encrypted and received without issue. Anyone who send an email to those domains will not get any warning, they will not even know what is going on.

This both saves you money on IP Addresses and SSL Certs, also, its the only way supported by single IP email servers.

SNI is available but for web browsers.