For the tcsh shell

To enable mailx processing, do the following:

Set up a system startup file, /etc/mailx.rc, which contains variable values and definitions common to all shell users. The IBM-supplied sample is in /samples/mailx.rc. Copy this file to /etc/mailx.rc.
If you use a system mailbox directory other than /usr/mail, identify it in the $MAIL environment variable in /etc/csh.login. See Customizing /etc/csh.login.

Users can give names to mail files using variables in $HOME/.login or they can use files with the default names. See Customizing /etc/csh.login.