TYPO3 Core

Digging into this topic I had to find out that RFC2822 also allows several other characters like "*" and "^" in the local-part of an address. (Section 3.2.4, 3.4.1).
Furthermore the "." is only valid if its not at the beginning or end of the local-part. The current regex also does not reflect this. And the plus-sign has (if used) sometimes only the meaning of a tag-mechanism for filtering.

There is a nice article at http://en.wikipedia.org/wiki/E-mail_address and especially for the regex-matching I found http://www.regular-expressions.info/email.html . Tons of other articles can be found on the net.

Your patch is correct so far, no question. I personally think (but that does not mean anything) a subset of the spec will suffice, most people don't use any special characters anyway (except . and -), so I would prefer to stick to the current implementation. A real change would have to come up with a quite complicated regex, and even then this would either be a monster or a subset of the spec.

I'm aware that the regex is far from perfect. I'm asking to add the '+' sign specifically because some of our users make use of the '+' for tagging of mailaddresses.

I have tested your patch on trunk (with the tipafriend ext) and will give you a +1 on reading and testing if you submit it.

Resolved as duplicate of #20285

t3lib_div::validEmail now uses native PHP filter in 4.3