Unknown command

does anyone have an idea what this error is about? it occurs from time to time during backup of labels... unfortunately very often recently.

Error: IMAP: FETCH command error: BAD ['Unknown command z15if12122807fam.73']

thx

right before this error,

right before this error, there are lot's of reconnections in the log:

Network error occured, disconnected
Trying to reconnect (1)
Reconnected!

those network errors only happen during the label backup phase as well. the mail backup phase is clean and stable. i don't know if it's the same problem as the unknown command or not.