Lots of programmers try to write regular expressions to validate e-mail addresses, but it&#x27;s extremely difficult for them to get it right, because valid e-mail addresses as defined by RFCs 822 and 5322 fall outside the set of formal languages describable by most regular expression libraries. See this fun stackoverflow answer [0].<p>[0] <a href="http:&#x2F;&#x2F;stackoverflow.com&#x2F;a&#x2F;201378" rel="nofollow">http:&#x2F;&#x2F;stackoverflow.com&#x2F;a&#x2F;201378</a>