I am running SBS 2008, using MXtool Box to reslove DNS issue its showing they were able to connect to your mail server on port 25, but the diagnostic session took longer than expected. This could indicate that your email server is under heavy load.
Here are the levels for which we issue warnings and alerts:
Over 5 Seconds: Warning
Over 8 Seconds: Alert
Having this warning on your lookup does not necessarily mean that you will have a problem receiving mail. It is simply a warning that things are less than optimal. This could end up causing users to experience delays with inbound mail.
It is also possible your server is “Tar pitting.” Tar pitting is a technique used by some email servers to slow down spammers. The idea is that legitimate senders will wait longer to establish a connection than spammers will
What can be done about this?