[Exim4U] are outgoing mails scan by Clam and SA

Dear List, our network administrator are having issues with smtp traffice (we are an ISP) most of our customer's IP are sending spam, this is giving a bad reputation on our IP's on the rbl's. they are suggesting that all smtp traffic from our customers be forwarded to our mail server and the the server will check for malform mails, scan the mails and then further forward them to their destination. my question is: 1. those exim4u scan outgoing mails 2. is it a good idea to go about this setup? 3. is there any other best solutions. Thanks Kebba