I can also vouch for Migadu. I've been using it for 6-7 years with 4 different domain names because they only charge for usage; not per domain or user. The few

I can also vouch for Migadu. I've been using it for 6-7 years with 4 different domain names because they only charge for usage; not per domain or user. The few times when I contacted support they were also very helpful.