They’re a little swift about locking accounts for spam suspicion. They did so to mine before I had sent a single mail and demanded I contact them through the (locked) mailbox.org mail to resolve it. Had to dispute the charge with my credit card.

My vote goes to Migadu. Slightly complicated UI, but it all works, and they don’t lock accounts before they have seen any indications of misuse.

Runbox is OK too, though they don’t support bouncing inbound mail based on recipient address, so less useful with your own domain.