Q4.0.9: rmail or VM gets an error incorporating new mail.

Quoting the SXEmacs PROBLEMS file:

rmail and VM get new mail from /var/spool/mail/$USER using a program called movemail. This program interlocks with /bin/mail using the protocol defined by /bin/mail.

There are two different protocols in general use. One of them uses the flock system call. The other involves creating a lock file; movemail must be able to write in /var/spool/mail in order to do this. You control which one is used by defining, or not defining, the macro MAIL_USE_FLOCK in config.h or the m- or s- file it includes.

IF YOU DON’T USE THE FORM OF INTERLOCKING THAT IS NORMAL ON YOUR SYSTEM, YOU CAN LOSE MAIL!

If your system uses the lock file protocol, and fascist restrictions prevent ordinary users from writing the lock files in /var/spool/mail, you may need to make movemail setgid to a suitable group such as ‘mail’. You can use these commands (as root):

chgrp mail movemail
chmod 2755 movemail

Installation normally copies movemail from the build directory to an installation directory which is usually under /usr/local/lib. The installed copy of movemail is usually in the directory /usr/local/lib/sxemacs-VERSION/TARGET. You must change the group and mode of the installed copy; changing the group and mode of the build directory copy is ineffective.