At least share the FILENAME and any ODS statement information. Ideally it would be best to COPY/PASTE the SAS-generated log output where the fully-expanded SAS code is generated and any diagnostic messages are displayed. Someone may try to guess that you do not have a domain name listed in your destination EMAIL address, based on the ERROR you have shared in your post -- best to be sure by sending the log output intact for good feedback. Also, SAS version info with service pack or "phase" (SAS 9.2) helps a lot as well.
Lastly, the presumption is that you can send EMAIL with the same format using some other EMAIL client on the same machine with VISTA, right?