Greetings, Our mail server runs UW IMAPD on Debian Linux. For many users, our MTA (exim4) use ~/.procmailrc to move mail to ~/mbox when it comes in. For some other users who do not have a .procmailrc in their ~ , it seems that mail stays in /var/spool/mail/username until they connect via IMAP, at which point IMAPd moves the mail to their mbox (according to syslog): Example from syslog: Apr 13 11:09:36 caen imapd: Moved 1638 bytes of new mail to /homes/user/mbox from /var/mail/user host= examplehost.com [18.104.22.168] For some other users still, the mail stays in /var/spool/mail/username, IMAP functions normally but the mail stays. I am trying to figure out why IMAPd moves some users mail to their mbox and keeps other users in /var/spool/mail . Thank you, Kevin Long Your binaries were compiled with EXTRADRIVERS=mbox This means that if ~/mbox exists, then whenever a program linked with c-client (like imapd, ipop3d, alpine) accesses the mail spool (/var/mail/username) mail is copied from there to ~/mbox. The combination of those two files is INBOX. If ~/mbox does not exist, then mail is processed as expected.