This is ... a bone of contention; basically, the email address is perfectly valid - but the browsers can't agree on what the correct encoding is - whether it is `foo+[email protected]` vs %-encoding, and no single encoding works on all browsers. We've gone with the former for now, as it has wider compatibility - BUT I was very disappointed that when google added an official `mailto:`  handler, they broke this (so it comes in as `foo [email protected]`), when every other browser works the other way. FWIW, the previous unofficial handlers in gmail were also broken.

This is discussed more http://webmasters.stackexchange.com/questions/15920/should-plus-be-encoded-in-mailto-hyperlinks, and AFAIK the conclusion is: it is ambiguous spec.

But! Try it in IE/FF/Opera/Chrome etc to see it work/not-work. Sigh.