filelock

How come procmail is ignoring a .lock file?

I have in /var/spool/mail/

-rw-------   1 contact  contact      3600 Aug 21 14:22 contact
-r--r--r--   1 contact  contact         1 Aug 21 14:21 contact.lock

So why can mail still come in to user contact, completely ignoring the lock
file?

Sincerely,
Peter Bleickardt