permission and group being changed on mail files

I installed procmail 3.11pre4 no a BSDI system and noticed that some users
mail files (mail is kept in a directory called /var/mail) are getting
their permissions changed to 660 from 600 and their group ids are being
changed from user to mail.  

Why is procmail doing this and how can I stop it?

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Alex M.
Asst. Systems Administrator
Feist Systems, Inc.
email: alexm(_at_)feist(_dot_)com
web:   http://www.feist.com/~alexm
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