I've started seeing the following error in mail.err for precisely one user on precisely one domain:

Error: mkdir(/var/mail/vmail//jeff/mail) failed: Permission denied (euid=1000(jeff) egid=1001(jeff) missing +w perm: /var/mail/vmail/, dir owned by 4000:4000 mode=0755)

Error: Mailbox INBOX: Failed to autocreate mailbox: Internal error occurred.

In mail.log I see a bit more:

Warning: Failed to parse address from `From_'-line: Missing domain
Error: mkdir(/var/mail/vmail//jeff/mail) failed: Permission denied (euid=1000(jeff) egid=1001(jeff) missing +w perm: /var/mail/vmail/, dir owned by 4000:4000 mode=0755)
Error: mkdir(/var/mail/vmail//jeff/mail) failed: Permission denied (euid=1000(jeff) egid=1001(jeff) missing +w perm: /var/mail/vmail/, dir owned by 4000:4000 mode=0755)
Error: Mailbox INBOX: Failed to autocreate mailbox: Internal error occurred. Refer to server log for more information.
save failed to open mailbox INBOX: Mailbox INBOX: Failed to autocreate mailbox: Internal error occurred.

And yet there's no apparent problem sending and receiving mail for user jeff, for all domains handled by the server.  Other users have no issues.  The /var/mail/vmail/ hierarchy is all owned by vmail:vmail (4000:4000) and directories are all 0755.

I suspect a red herring except it's been continuing for a week now.  I was reading this page (following some searching), but it doesn't seem pertinent in the end.

https://wiki2.dovecot.org/MailLocation/mbox#A.2BAC8-var.2BAC8-mail.2BAC8_dotlocks

Any suggestions what this might be?

-- 
Jeff Abrahamson
+33 6 24 40 01 57
+44 7920 594 255

http://p27.eu/jeff/
http://mobilitains.fr/