best regular expression for validating email addresses? - What is the

Maybe you're wondering why there's no "official" fool-proof regex to match email addresses. Well, there is an official definition, but it's hardly fool-proof.
The official standard is known as RFC 2822. It describes the syntax that valid email addresses must adhere to. You can (but you shouldn't--read on) implement it with this regular expression:

(?:[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*|"(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21\x23-\x5b\x5d-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])*")@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?|\[(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?|[a-z0-9-]*[a-z0-9]:(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21-\x5a\x53-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])+)\])

Java program for regex

import java.util.regex.*;

class regexSample 

{

public static void main(String args[]) 

{

//Input the string for validation

String email = "xyz@hotmail.com";

//Set the email pattern string

Pattern p = Pattern.compile(" (?:[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*|"
         +"(?:[\\x01-\\x08\\x0b\\x0c\\x0e-\\x1f\\x21\\x23-\\x5b\\x5d-\\x7f]|\\[\\x01-\\x09\\x0b\\x0c\\x0e-\\x7f])*\")"
            + "@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?|\\[(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?|[a-z0-9-]*[a-z0-9]:(?:[\\x01-\\x08\\x0b\\x0c\\x0e-\\x1f\\x21-\\x5a\\x53-\\x7f]|\\[\\x01-\\x09\\x0b\\x0c\\x0e-\\x7f])+)\\]");

//Match the given string with the pattern

Matcher m = p.matcher(email);

//check whether match is found 

boolean matchFound = m.matches();

if (matchFound)

System.out.println("Valid Email Id.");

else

System.out.println("Invalid Email Id.");

}

}

http://stackoverflow.com/questions/201323/what-is-the-best-regular-expression-for-validating-email-addresses/4554294#4554294