Controlling the "From:" access control

["Mark Cartwright" <Mark . Cartwright @ intcx . com>]

I have a list that currently only accepts posts from a small (text) list of folks; this part works well.

However, there seems to be nothing stopping some arbitrary person from manipulating the mail header for the "From:" address and inserting an "accepted" email, thereby allowing anyone with knowledge of a valid post user and how to modify the From: mail header from posting to any list.

Is there some other facility, shy of denying all inbound SMTP traffic, of gaining some higher level of control over who can actually send to the list?

Thanks for any replys.

For completeness, my realivant version information:

Majordomo v1.94.5
Sendmail v8.11.7+Sun