Beginning with V8.12 sendmail, it is possible to screen email based on sender and recipient address pairs stored in the access database. One use for such a method might be to prevent one employee from receiving mail from another employee. Another use might be to prevent a pseudo-user, such as admin, from receiving spurious reports from another user, such as bin. Yet another use might be to reject spam mail to a mailing list.

This compat_check feature is described in full in Section 7.5.7.