- POSIX regular expressions are deprecated
As you may have noticed, since PHP 5.3 the use of POSIX regular expression functions is deprecated. The class was changes to use PCRE functions instead.
The syntax of the default e-mail address validation remains the same. The class converts the regular expressions to make them work with PCRE functions. So you do not need to change your code if you change the default e-mail regular expression.
- GetMXRR function in Windows
If you are using PHP on Windows, you may have noticed that now PHP 5.3 implements the GetMXRR. This function is used to determine the SMTP servers of a given e-mail address domain.
Therefore, if you use Windows on PHP 5.3, you no longer need to use alternative implementations of the GetMXRR function that used to be assigned to the getmxrr class variable. Just do not change that variable so the class uses the regular GetMXRR function implemented in PHP.