$re = '/^([_A-Za-z0-9-\\\\+]+(\\\\.[_A-Za-z0-9-]+)*@[A-Za-z0-9-]+(\\\\.[A-Za-z0-9]+)*\.[A-Za-z]{2,})$/';
$str = 'ashish.verma724@gmail.com
alok%#%$#%$#%$#%$%';
$subst = "";
$result = preg_replace($re, $subst, $str, 1);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php