Does anybody have any recommendations on how to filter outgoing email against a custom black list? For example, I have a list of around 400,000 email addresses that I do not want to send email to. Currently the email administrator says he is using a Sieve script to filter the outbound email but using it to filter is too slow. We are running Linux and most likely Postfix and also a commercial MTA which was called Ecelerity but is now part of Symantec Message Labs.
Is there a tool that is better/faster than Sieve for filtering outbound email?