The subject condition is generally the result of configuring the 'use DNS' feature at Exchange Administrator / Internet Mail Service / Properties / Connections. This is only designed to handle a full-time connection to the internet.
To work-around this issue, use the Forward all messages to host option and specify an ISP relay server, which is also faster.
NOTE: If you are using the SBS Internet Connection Wizard, you will have to change the 'use DNS'
feature after the wizard completes.