Interesting. My husband's email raw message view DOES show the actual HTML of the email. Only the very last link to the store at the bottom shows up with anchor tags around it. My sign up link and the mailto link for the store (part of the original ZC code) do NOT show up with anchor tags around them even though they are clearly there in the PHP.

I've decided to "solve" this problem for now by just putting "please sign up at www.example.com" in the text string there. Email programs seems to recognize any text starting with www as a link and display it as such. So that's gonna have to be good enough unless someone comes up with other ideas for me. I have other brick walls to go beat my head on!