I would put Migadu more in the hobby category...they seem pretty upfront about their drawbacks: https://www.migadu.com/en/drawbacks.html

If you have a ___domain where those drawbacks aren't showstoppers, you might also look at Yandex hosted email. Can't beat the price (free), it has decent storage (10GB) and the limit for sending is 500/day[1].

See: https://___domain.yandex.com/domains_add/

[1]https://yandex.com/support/mail/spam/sending-limits.xml

Those drawbacks are also valid for any other small provider. Fastmail also has the problem of mails classified as spam. Really any service except the biggest 3-4 have occasional reputation problems.

The difference is just that Migadu is honest about it.

There's also zoho.com that offers free mailboxes with custom domains.

My primary email is not where I would start grabbing some pennies in front of the steamroller.

Agreed. Service looks good, but been with Fastmail forever and not willing to risk a change at the moment.

Would have not expect you to change either. Fastmail is awesome and a lot of respect for them. We're trying to learn from them all the time.

I'd classify Migadu in a different category. If you run multiple projects or just need extra addresses fast at no extra costs, you'd probably not go for FastMail. I can clearly see using them both.