Just checked out Migadu. Their support page is pretty sparse, but it looks to me like they fail on the same criteria Fastmail fails on, which a sibling commenter mentioned and I replied to here:
https://news.ycombinator.com/item?id=30397414Believe me, I am also a big proponent of open software and standards. But when the open options all seem to be inferior, then it doesn't make sense to go with them, especially when they have to support a business.
(also, the name is pretty funny to me, as 'mi gadu' is slang for 'oh my god' in the Netherlands :P)