Hi

Had problems with my iCloud email since a couple of days.
Constantly getting a popup message to fill in my password. (was working before so had no clue what caused the issue)

So after a fight of a couple of hours and a lot of changing settings / uninstalling apps (as was instructed in this thread) i was able to solve the issue.

Apparently I had to change the server settings, so for those of you that are struggling with iCloud servers, here's the solution that worked for me:

Incoming mail server (iMap)
imap.mail.me.com (this was new to me)
SSL: YES
Port: 993
user: user@me.com
passw: your iCloud passw

SMTP
smtp.me.com
SSL: NO
Port: 587
Authentication: Plain Passw
user: user@me.com
passw: your iCloud passw

Good luck with it!