SBS can be configured to override the default Dial-up settings of the Internet Mail Service.
To Send and Receive Now, use SBS Console / Tasks / Manage Electronic Mail / Send and Receive Now.
If you have a full-time or router connection, Send and Receive Now simply wastes resources by cycling the Internet Mail Service. To disable this feature, use Regedt32 to navigate to:
Double-click Mail_Retrieval_Method in the right hand pane and set the string value to None.