Did you look at CPAN?

If not, why would you post here without a basic search of CPAN?

If you did look at CPAN and did not like a particular module, you should mention that in your post.

You also should explain what your mail server is and more importantly what format the queued mail is stored in. That would help narrow down a suggestion (I know what I mean. Why don't you?).

As to the problem of too much spam (I'm assuming) check out Greylisting. It's quite effective without much of a server load. There are several solutions and (from my experience) very easy to setup. If you are worried about the delay affecting your customers, you can setup an whitelist for your customers (avoids the delay) or set it up just to run on the weekend.