There are many things that could affect this. In your location doc, do you have the field on the Mail tab for sending to the Internet in MIME Format? Also, your Global Domain document could be the issue. This is dependant on how you connect to the Internet and your lookups. You could bring in a SMTP expert to help you out. I can't give you an answer without first seeing your environment. I have done this many times before, and it shouldn't take more than a few hours to sort out. Good luck.
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