I agree on the subject line (which is "Verify your email address") and that the mail is sent from "Google Scholar Citations", but as it was possible to include arbitrary CSS files, the content could be changed to pretty much anything... Although there was a length-restriction on the user's name, there were two other fields that weren't escaped properly and thus could be used to insert more HTML-content.
Ah, yeah smartphone and desktop apps don't do js(afaik) - but the web-browser access is still big. If gmail's web interface went down for a day, I think a lot of people would notice.
My guess: the WYSIWYG editor uses its own HTML parser and filter, written in JavaScript, that has some O(n^terrible) corner case that your paste test is hitting.
