I wanted to find a regular expression to validate e-mail addresses, but when I searched I found dozens of slightly different versions of the same expression. Almost all of them had people leaving comments about how it failed to validate or invalidate some rare but completely valid/invalid address syntax. But dispite all the criticism, I couldn't find a definitive "best" expression. So, I setup arrays of some of the most promising expressions as well as a (hopefully) complete sampling of valid and invalid addresses. It's my philosophy that it's better to accept a few invalid addresses than reject any valid ones, so I'm shooting for 0 false-positives and as few false-negatives as possible. If you have any sample addresses or expressions that you think should be added to the list, or if you can further improve the best expression please e-mail me at:

Conclusion:
Geert De Deckere from the Kohana project has developed a near perfect one:
/^[-_a-z0-9\'+*$^&%=~!?{}]++(?:\.[-_a-z0-9\'+*$^&%=~!?{}]+)*+@(?:(?![-.])[-a-z0-9.]+(?<![-.])\.[a-z]{2,6}|\d{1,3}(?:\.\d{1,3}){3})(?::\d++)?$/iD

Notes:

• There's no perfect regular expression to validate e-mail addresses
• Table of valid and invalid characters in the local part of an e-mail address
• Some characters (like the ampersand, apostrophe, asterisk etc) are technically valid, but can cause problems due to their significance in operating systems, programming languages and applications and therefore shouldn't really be used. I've just used my judgement on whether they should be treated as valid or not.
• Some of these are dependent on being executed using case-insenstive regex functions.
• This page uses PHP's ereg() and preg_match() functions, but some of these will work with JavaScript and other languages