Wystarczy, że zastosujesz JavaMail API//java.sun.com/products/javamail/
Względnie jeżeli chcesz napisać samemu walidator zgodny ze standardem wystarczy, że użyjesz tego oto prostego wyrażenia regularnego do sprawdzenia poprawności adresu:
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Proste ;)
żródło: http://www.ex-parrot.com/pdw/Mail-RFC822-Address.html