The file contains a path to a custom mailbox-file

id:content-path-file

This error incidates that the qmail file is configured with a path to a mailbox file and thus bypasses the mailsetup.

You will need to create a real mailbox with uberspace mail user add ... and import your mails from the mailbox file if you want to keep them in the standard mail system.

Error

Error: This configuration is probably not working as expected in the standard mail system. This is why you should recreate this mailaddress yourself using the uberspace mail commands.