I posted about Dynamics GP and 64 bit support last year. As per the technology requirements for Dynamics GP – for the e-Email feature -
E-Mail Functionality Feature
As you can see 32 bit Office is required. So if you are getting the "connection to the mapi server not available" error, and Outlook is working fine, you need to check your office version. If you have the 64 bit version install, you need to uninstall it, and re-install 32 bit Office.