I've been using Migadu for a low-moderate throughput inbox (within their micro tier limits) in the US and the IMAP4 performance is kinda awful sometimes. I'm not sure why :(

Ended up dropping migadu. Lots of things I liked like the configuration but it was fairly expensive for what you got. After 3 years of paying, I once went over my outbound quota and couldn't send email for the day.

Tried them with a domain that gets a bunch of spam, unfortunately their filtering is not as good as others like Fastmail it seems.

Migadu is fantastic if you can live with their daily limits.