Among these runbox is quite good and my friend has used migadu for a few years and likes it even though he says the "soft" limits still make him uncomfortable even though so far he has never hit them; so I guess that should be fine. Posteo doesn't support custom domains (I've used them and otherwise they are good). I wouldn't go with Proton ever. Mailo seems new - never heard of them. Would love to get a review.

mailbox.org can be avoided if you need to send and receive emails from domains where the mail admins might not be email admin savants and/or privacy activists (sometimes that's not a choice in case of Govt services etc and you may not live in a country when you can get those changes done). Also, if you ever face an issue and send them an email, expect the reply to come in weeks (if you are lucky) and that too a flippant (sometimes even terse) nothing-mail and then if you respond the cycle repeats until you give up.

Splendid, thank you. the european-alternatives.eu is exactly what helped! Appreciate it!