Tee hee...... a posting from a microsoft.com address...... we are starting to break in boys and girls🙂
This is not really an email forum, but......... Does this problem occur only with that specific customer? Have you tried including your address as a CC or BCC to test if the messages are being sent properly formatted from your end? If you get a properly formatted email this way, the problem is most likely on your customer's end in either his/her mail client or server. Otherwise, I'd suggest talking to the tech support/network admin staff at MS. HTH.
geoff