My postfix server was logging this error : postfix/smtpd: lost connection after AUTH from unknown[71.00.18.255] The outlook 2003 user was getting successful mail sent message but the messages were lost and never made it to the recipients. Postfix never saw a message from the SMTP connection. I searched long and hard and finally found the problem: AOL antivirus. It is listed in Microsoft's support database but that wasn't where I went to look for postfix problems, I came here. So I thought I'd post this to let you know the problem. AOL antivirus scans emails and if the message has more than four recipients, the message is never sent but outlook thinks it was. It affected Outlook 2003 for me. Disabling AOL's email scanner fixed the problem. The real solution is to stop using AOL as it is an inferior product at a high price but that's out of my control.