SQL Server CLR function to improve performance of validating email addresses

When you send e-mail to large lists, validating the e-mail addresses before sending out the e-mail is worth doing to prevent having mail rejection messages clog up your mail server. I had been doing the validation with a T-SQL User Defined Function (UDF), but it was getting too slow as the number of e-mails grew. I needed a faster alternative, what options do I have?