G?tz Reinicke writes:

mail_location = mbox:~/:INBOX=/var/mail/%u ... Namespace inbox: type=private, prefix=, sep=, inbox=yes, hidden=no, list=yes, subscriptions=yes location=mbox:~/:INBOX=/var/mail/rechnungseingang-animationsinstitut Feb 27 17:02:11 imap(rechnungseingang-animationsinstitut): Error: user rechnungseingang-animationsinstitut: Initialization failed: Namespace '': Home directory not set for user. Can't expand ~/ for mail root dir in: ~/:INBOX=/var/mail/rechnungseingang-animationsinstitut

Hmm, I don't have a trialing '/' in my mail_location, so maybe you can try leaving it off too just to check.

mbox:~:INBOX=/var/mail/%u

Also, is your home directory well defined in your userdb? Check output of

doveadm user rechnungseingang-animationsinstitut

Joseph Tam jtam.home@gmail.com