I mentioned this as a bug two months ago or something like that. I even mentioned a quick fix to be a bit more standards compliant (which would let the above mentioned email be entered).
There is an RFC (used to be 822, but has been superceded by 2822) that clearly states what is allowed within an adress. In RFC 822 you could have any word-character and dot (.) as long as it doesn't begin or end with a dot. A word character is the normal english alphabet, upper and lower case, numbers as well as "-". So with the old RFC822 it is perfectly okay to end the mailbox part (before @) with -.
With RFC2822, which should now be used, even more characters are allowed. Basically any other alphabetic characters in the standard ASCII table (even foreign ones), as well as a bunch of separation characters: !#$%&'*+-/=?^_`{|}ยด~
You still can't begin or end with a dot though, but any of the above characters are OK.
Don't know how many mail servers comply with the new RFC though, since it was published in April 2001, but I'd say threads is as good a place as any to start using it.
I can write the regex needed to make it work with either RFC 822 or RFC 2822 depending of what might be best.
