Tom wrote:

Your message got me to thinking and I suspect that Outlook's built-in
spam detecting rules are superceding my rule.

The Junk E-mail filter runs before the Rules engine. You can't change that.
You can, however, as you say, reduce the sensitivity of the Junk E-mail
filter or, if you find those messages, add the sender to your Safe Sender's
list (or in the case of a mailing list, add the list address to the Safe
Recipients list).
--
Brian Tillman [MVP-Outlook]