Things that confuse our regex before the @:

• dots
• numbers
• underscores
• dashes
• plusses
• ?

Other issues:

• add "un" as a 'country' (and there must be a web page somewhere with the canonical list of top-level domains, maybe this: http://www.iana.org/domains/root/db or even better would be a blog that posts as new ones are added)