I've seen http://www.webassist.com/forums/posts.php?id=37242
One person has a .menu email address and the site wouldn't allow this. Having carried out the first part on the page above, the address can now be added (I couldn't find any instances of the other code in the entire site - perhaps the extension has been updated since then).
However, when that address is the recipient of an enquiry on the attached page, the email doesn't work - all others do.
Is there a global fix available?