I needed a mail server for a few custom email addresses from several domains that I own. There are some 6 domains and 10 custom email addresses.
Multiple email domains can be hosted on a single mail server. They are called virtual domains. Basically firstname.lastname@example.org and email@example.com can be directed to mailserverdomain.com. Clients from domain1 and domain2 connect for email service to mailserverdomain.com
This configuration moves my email addresses from outlook.office365.com which charges $5.- / month / email account. Totals to a sweet $50.- monthly. That’s $600.- a year which I could use for something else.
This results in a Mail Server capable of hosting multiple domains with multiple emails accounts. In fact it is running in my home office on a Raspberry Pi box!
If you want something like this but skip about 200+ lines of instructions, let me know, I’d be happy to help!