Procmail does not create valid mboxes

[FrithjofEngel]

Hello

either my procmail or my mutt configuration is broken, i cannot read my mbox-mails.
Mutt says "File is not a mailbox". This is strange, as I used this configuration on my former
system.

My .procmailrc looks like this (/etc/procmailrc is empty):

[papal_authority]

I had a similar problem. Maybe check out this thread: https://forums.gentoo.org/viewtopic.php?t=166410&highlight=