Don't user eregi (or any other POSIX function) unless you really have to. The preg_match() (PCRE functions) are faster and binary-safe, to sum up the PCRE functions are better than the POSIX functions.

Your regexp is unfortunatly incomplete (doesn't match all possible addresses) but hey, there is as far as I'm concered only one which does (were situated here before it got removec; http://public.yahoo.com/~jfriedl/regex/email-unopt.pl) but yours matches a bit to few for my taste.
It won't match addresses such as james+blunt@example.com or james&blunt@example.com (they are both valid addresses).

Just some thoughts.

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http://jiart.org/
My digital playground with it's own sandbox.
Well anyway, I love programming

For an RFC822 compliant email address matcher check out this article or you can download the source.

Wait, you can put +'s in an email address? Oo; New to me. For real?

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...to allow for the foo+bar@foo.com format.

It's really handy, yet so often forgotten.