When setting up 
Maildir in Debian 5.0, getting the generic 
mail applications working correctly can be tricky.
- Install the 'mailutils' package, not the bsd mailx package.
 
- Do not touch the mailutils /etc/mail.rc file; there are some promising looking variables here like 
mailbox-type but these do not do what is desired. When the MAIL environment variable is set correctly mailutils will automatically detect the maildir box type. 
- Do not touch /etc/login.defs; the promising looking lines in here are deprecated.
 
- Edit files in 
/etc/pam.d, changing the pam_mail.so lines as shown (assuming ~/Maildir as the selected location):
  
  - login: default login shells
  session    optional   pam_mail.so dir=~/Maildir standard
   
  - su: set up for proper MAIL when using su; nopen does not show 'new mail' message
  session    optional   pam_mail.so dir=~/Maildir nopen
   
  - sshd: set up MAIL properly when logging in with ssh; this line probably has a noenv by default which needs removed to set this properly
  session    optional     pam_mail.so dir=~/Maildir standard