OK gotcha. Here is my current topology. Our SMTP relay box (Barracuda) is what gets outside mail first. Then it goes to Exchange (only one Exchange server - 2003). BOTH boxes are on the inside of our PIX and only the Barracuda has its internal address mapped to an external address. I did set up tar pitting on Exchange although I'm not sure how useful that will be since technically, the only other computer that connects to it SMTP-wise (besides internal domain clients obviously) is the Barracuda box. I am not too sure if the Barracuda device has any sort of tar pitting but that is something I will have to take up with them. In any case, thanks so much for the info John, I truly appreciate it! ________________________________ From: John T (Lists) [mailto:johnlist@xxxxxxxxxxxxxxxxxxx] Sent: Thu 1/5/2006 6:09 PM To: [ExchangeList] Subject: [exchangelist] RE: Some Advice Please http://www.MSExchange.org/ If it is a harvesting or dictionary attack, your best bet is an automated way to temporarily block connections from an IP after x amount of invalid recipients or tarpit the IP after x amount of invalid recipients. Some one else has posted a couple of links of how to do this on Exchange, but IMHO you want to do this before your Exchange server unless you a small shop and do not have other resources. My clients Exchange servers sit behind my e-mail server which is acting as a gateway for them which that server sits behind 3 MS SMTP servers with ORF running. ORF is actually a very good product that is growing but does not get mentioned much. It can install on any server running IIS as it works directly with the IIS SMTP service. A harvest attack is where the attacking server(s) will "send" an e-mail to every possible address at your domain from a through zzzzzzzzzzz (you get the idea) to find out which are valid addresses. The proper way to fight this is either block the IP after so many invalid recipients or to tarpit which means waiting 30 to 60 seconds to respond with a 5.1.x indicating an invalid address. John T eServices For You -- No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.1.371 / Virus Database: 267.14.13/221 - Release Date: 1/4/2006 -- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.1.371 / Virus Database: 267.14.13/221 - Release Date: 1/4/2006 -- No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.1.371 / Virus Database: 267.14.13/221 - Release Date: 1/4/2006