for some reason Outlook is trying to ask for a receipt BEFORE the message is sent on a wireless system! If the receipts aren't given, that could be why it't rejecting your e-mail.
I keep off wireless systems and just hard-wire anything I need (except of course the internet).
When hitting 'reply' to a message in Outlook frequently get the above error message only when connceted via wireless systems at office and home and wireless systems are not same. Do not get error message when connected via modem. Have checked email accounts folder and all seems correct including "outgoing server requires SMTP authentication" which is checked in outgoing server window. Using windos XP, Outlook 2003 on an IBM laptop. What to do sionce email responses are being rejected immediately by my computer and not the email server when this happens.