Another vote for migadu. I've used migadu for my family between two domains on their cheapest plan. I've been very happy with it. Their webclient while functional is a bit barebones so we use phone email + emclient on laptops with nextcloud handling contacts and calendar.
Are you using Migadu on a daily basis? If so how is it?
I use Migadu on a daily basis and the experience is absolutely incredible. The UX is very satisfying: everything is well described, it's a simple website and seems to just work. It serves a bit as a buffer for all my email traffic so I can use any client I like (even redirect to gmail if need be). The pricing looks reasonable to me. Overall I can highly recommend this.