Unexpected IMAP response on iCloud accounts

[PhilippJMeyer]

I tried to obtain a certificate for my iCloud email but received following error:

Encountered exception during recovery: imaplib.IMAP4.error: LOGOUT command error: BAD [b'DONE is the only command allowed after IDLE’]
An unexpected error occurred:
imaplib.IMAP4.error: Unexpected IDLE response: b'* 11 FETCH (UID 10060 FLAGS (\\Seen))’

Here’s the log file: letsencrypt.log

As far as I know this only happens with the iCloud Mail Server.