So you ask: What is tar pitting?

IMHO,  tar pitting is a very suitable way to stop misuse of your Windows 2003 / Exchange 2003 SMTP Virtual Server by delaying SMTP responses for 5.x.x errors. This efficiently stops DoS and harvesting attacks on your SMTP servers.

For example: Hacker A continously sends mail to your server, named yourserver.mail.net, the simple purpose being to gather valid e-mail-addresses from your domains. This Brute-Force-Attack is called a "Directory Harvest Attack". 

Have a look at this telnet-screenshot, where a simple SMTP-communication is depicted: 

Normally, this kind of communication would just take a view milliseconds of time on your SMTP server. With tar pitting enabled, SMTP Virtual Server will freeze the connection for a configurable  amount of time before returning "550 5.7.1 Unable to relay". More...

Tired of Outlook Web Access blocking that attachment you would need most urgently, just because it has some weird extension?? Fear not, for this behaviour is customizable.

Fire up regedit on your OWA Server, and head for HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSExchangeWEB\OWA

It should look pretty much like the screenshot here: 

More...