[Exim] permissions on /var/spool/mail/mailbox

I have run into problems because procmail wants to enforce the following
permissions:

-rw-------   1 pollywog mail         5067 Oct 25 20:25 pollywog

but Exim seems to want:

-rw-rw----   1 pollywog mail         5067 Oct 25 20:25 pollywog

on /var/spool/mail/pollywog

Can I make Exim conform to the stricter permissions and can I do it without
recompiling Exim (via the exim.conf file ?)


thanks

--
Andrew