Cool, glad it's working for you. Interesting quirk, right? I bet a lot of others don't quite realize what's happening.
Success!
Problem solved, thank you for the assistance.
Overwriting the token in the HTML editor with
<a class="mktNoTrack" href="mailto:{{Lead.Email Address}}">{{Lead.Email Address}}</a>
solved the problem. Token data values follow the colour style as the other links in the email and footer, making it a much nicer looking email.