When performing test on a Microsoft Exchange server, some tests will return a transaction time warning. For the most part this is not an issue and nothing needs to be done. This delay is intentional on the part of Microsoft Exchange to help prevent spam. The warnings are typically given when it takes more than 1 second for the SMTP connector to respond to the request. This process of delaying multiple mail requests is called tarpitting.
If this warning bothers you, there is a change that you can make that will fix the Transaction time warnings for Exchange 2007 and 2010.
Diagnosing e-mail issues is often a time consuming task. Having your e-mail address, especially a corporate domain, blacklisted on a private list is even more troublesome. Each vendor has its own process and Comcast has their own as well.
Reporting Blocked Email
The SMTP Server Connection Diagnostics Tool is a free utility will enable you to troubleshoot SMTP Server issues more easily than using telnet. It supports both open and SSL connections and contains a built-in library of commands such as EHLO, DATA, RCPT TO, etc.. Nothing to install, just run the executable and step through your commands.