I just pay Hetzner 2.50-ish euros for their cheapest mail hosting offer and call it a day. I did self-host mail for quite some time, it was a huge PITA to set up and keep working. Every now and then I even had issues with my mails not being delivered to outlook addresses (f u M$), so I just gave it up and switched to Hetzner. Their cheapest plan even includes one domain, so depending on the domain you choose, it’s not even 1€ for the actual email hosting