[e mail]username@domain.com[/e mail] (take the space out of "e mail". I had to do that so it would show the code instead of the actual link.)
For a custom block you need to use the following HTML email link...
<a href="mailto:username@domain.com?subject=howdy">text to click on</a>
One of those two solution should fix the problem in most situations. I hope that helps.

