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[28575]: Moved 1638 bytes of new mail to 
/homes/user/mbox from /var/mail/user host= [] 

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 


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.