iCloud mail via IMAP stopped working

iCloud Mail via IMAP in Mail stopped working

Hi!

For a few months now I have been using iCloud mail configured in mail.app as an IMAP account, not as an iCloud account. The reason for this is that I want to use a different SMTP server, so outgoing mail has a different sender address. This has worked until a few days ago.

Now mail.app doesn't accept my user authentication anymore and asks for a password. I have entered it several times, and I'm sure it's correct. Logging into the account via icloud.com does work, and the same settings still work on my iPad and iPhone. Console doesn't log anything, only when I use the "check connection" feature in mail.app, there's an entry that says "Mail[447]: [<_LibSasl2SASLClient: 0x7fbebc0a76b0> mechanism: PLAIN security layer: no] Failed to start the SASL connection SASL(-1): generic failure:"

Things I have tried so far:
- deleting password from keychain - doesn't help
- configuring the account as an iCloud account instead of IMAP - works
- using the same settings in a (almost) fresh ML install - doesn't work
- using the same settings in Outlook - works
- using p01-imap.mail.me com instead of imap.mail.me.com - doesn't work

Any help with this would be appreciated. Thank you!

Regards,

Timo