email validation?

[aviendha]

I've written an ereg for validating an email. It works fine, but I keep wondering if I've covered all (or as many as possible) of the bases. This is my ereg:

if(!ereg("^([a-zA-Z0-9_\-\.]+)@(([a-zA-Z0-9_\-]+\.)+)(([a-zA-Z]{2,4})|([a-zA-Z]{6}))$", 
    $email_field))
{
     //error message
}

I'd be interested if anyone thinks I've missed something important, or even better, if someone can point me to a place that gives the syntax for valid emails, for example, can an email start with a number? Can the string after the @ have a hyphen or an underscore?

Thanks.

[seanpaulcail]

here's one froma book I have I trust, I've seen the exact same thing in some of Jessica Speigal's code

if (!eregi("^[a-zA-Z0-9_]+@[a-zA-Z0-9\-]+\.[a-zA-Z0-9-\.}+$", email))

Your's looks fine but if you're unsure allways g with a book example