OT: sendmail relay by IP unconditionally

[Furnish, Trever G]

First up, I realize this is OT but I'm not having any luck finding help
elsewhere.  Please feel free to reply directly to tgfurnish at herff-jones.com.
Sorry...  On the other hand, the only reason I'm looking to do this in
sendmail is because I also don't think MailScanner can do it.  I'd be happy
to be shown wrong on either point.

Given the following two servers:

1.2.3.4 Jeeves.com
5.6.7.8 Jacob.com

...I've always expected that putting the following line into Jeeves'
sendmail access map would allow Jacob to relay email through Jeeves
UNCONDITIONALLY - ie regardless of whether the messages matched a REJECT map
based on sender or recipient email address:

5.6.7.8 RELAY

I was wrong, as I recently painfully discovered. :-/

If Jeeves has the following additional lines in it's access map:
From:Jacob.com  REJECT

...then Jeeves will NOT accept any messages from Jacob.com, EVEN if they
actually are originating from 5.6.7.8.

In other words, the "From:Jacob.com REJECT" line takes precedence over the
"5.6.7.8 RELAY" line.  Is there any way around that?

I want to relay mail unconditionally from a specific ip address, and yet
still be able to block mail based on sender domain from other ip addresses.

I have a system which is an inbound-only relay for foo.com, which runs
mailscanner on the messages and passes them to firewall.foo.com.  The only
time that a message passing through the mailscanner box will legitimately
come "from someuser at foo.com" is when it comes from firewall.foo.com's ip
address.  Since users send spam back to the system for training with
sa-learn, that's a frequent occurrance.