Provided by: mlock_2007f~dfsg-5build1_amd64
mlock -- lock a mailbox
If libc-client.so is unable to create a mailbox lock file, it will call this program. This makes using the mailbox safe over i.e. NFS. There is no reason to call mlock yourself or through another program. It is setgid mail so there is no need to change the permissions of /var/mail to 1777.
No documentation other than this crappy man page,
mlock was written by Mark Crispin <email@example.com> This man page was written for Debian GNU/Linux by Jaldhar H. Vyas <firstname.lastname@example.org>