[kaijin]

Originally Posted by yennta

And then the Act On rule is invoked in the Outbox as "Act On Waiting" ?

Since that didn't work, I tried: in the outbox, I selected, "apply act on rule" and I chose the Act On Waiting rule. That didn't work either

The rule (and therefore the script the rule points to) is automatically triggered when you send your email. There is no need to assign it an Act-On keyword. The only reasons you need Act-On for this script is because Act-On creates the Outbox Rules tabe in Mail Preferences > Rules.