I'm thanking everyone, Alex.. I appreciate anyone trying to help!
Ok, so here's another question (giving you another chance!)
Is there a special format for sending more than one field value in the email body?
(I'm trying to make sense out of page 425 of the Admin guide, but it's a bit confusing...or I'm just tired. Not sure which)
When I send an email with both of these values, the first one works but the second one becomes a 'Log Comment' --
%EXTERNAL_SYSTEM_TICKET=999999
%REQUEST.ASSIGNEE=TZ26297