man : lockspool(1)
LOCKSPOOL(1) OpenBSD Reference Manual LOCKSPOOL(1)
lockspool - lock user's system mailbox
lockspool is useful for a client mail program to attain proper locking.
lockspool obtains a username.lock for the calling user and retains it
until stdin is closed or a signal like SIGINT, SIGTERM, or SIGHUP is
received. 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).
Typical usage is for a user mail agent (such as mail(1)) to open a pipe
to lockspool when it needs to lock the user's mail spool. Closing the
pipe will cause lockspool to release the lock.
/var/mail/username.lock user's mail lock file
The lockspool utility exits 0 on success, and 1 if an error occurs.
mail(1), mail.local(8), sendmail(8)
The lockspool program appeared in OpenBSD 2.4.
OpenBSD 4.9 September 3, 2010 OpenBSD 4.9