I have been self-hosting my mail server for the past 5 or 6 years with success. Recently my ISP decided to close port 25 so I have to use a third party to deliver my outgoing mail.

What cost?

It is hard to set up and you might need an SMTP relay since most ISPs close port 25. But it is feasible.

I have everything at home, including the mail server. The only third party to my setup is a SMTP relay. All on an Odroid H4+. With a backup server on a Raspberry Pi 4 at my daughter’s.