LOCKSPOOL(1) BSD Reference Manual LOCKSPOOL(1)
lockspool - lock user's system mailbox
lockspool [username]
lockspool is useful for a client mail program to attain proper locking. lockspool obtains a username.lock for the calling user and retains it un- til stdin is closed or a signal like SIGINT, SIGTERM, or SIGHUP is re- ceived. Additionally, the superuser may specify the name of a user in order to lock a different mailbox. If lockspool is able to create the lock file, "1" is written to stdout, otherwise "0" is written and an error message is written to stderr. lockspool will try up to 10 times to get the lock (sleeping for a short period in between tries). The lockspool utility exits 0 on success, and 1 if an error occurs.
/var/mail/username.lock user's mail lock file
mail(1), mail.local(8), sendmail(8)
The lockspool program appeared in OpenBSD 2.4. MirBSD #10-current August 13, 1998 1