Dovecot v2.3.4.1 Debian 10.3 mbox format - Error: chdir(/var/spool/mail/domain/user) failed: Not a directory

Hi colleagues,

I am trying to setup dovecot and have a strange problem. I configured it to:

#dovecot -n|grep ^mail mail_gid = mail mail_location = mbox:/var/spool/mail/%d/mailboxes/%n:INBOX=/var/spool/mail/%d/%n mail_uid = mail

And also setup exim4 to use it. I sent a test message and observe a mailbox file /var/spool/mail/domain/user, containing this message. But when I try to access dovecot with a client (thunderbird), client cannot fetch mail, and I observe error in the dovecot's log:

May 09 23:35:51 imap(user@domain)<25179><JNFIDz2ldeOsEAE3>: Error: chdir(/var/spool/mail/domain/user) failed: Not a directory

What is it, and how to solve it? Thank you.

Kind regards, Viktor