I created a new domain and added several mailboxes. Two of them appear to be working fine, but the other two are not receiving mail. Mail is being deferred with an error like this:
temporary failure. Command output: /usr/bin/maildrop: Unable to open mailbox.
A dive into strace gives me the clue that maildrop is trying to open the directory e.g. /var/mail/treasurer when it should be (virtually) /home/treasurer/Mail. But I have no idea why.
Despite this error, roundcube is able to open the mailbox and show older messages.
The problem may be related to the fact that on the two failing mailboxes I used rsync to bring over old mail from an old server. I checked permissions and ownership after and they look correct. FWIW I used the same procedure on a different domain earlier without encountering this problem.
Any suggestions? Thanks!