want to share the fixture that troubled the code. what we found that the c:\inetpub\mailroot\pickup directory does not have write access to IUSR. The reason is that CDO directly writes the mail file to SMTP servers’s pickup directory. It is not opening port 25 and sending a proper mail. probably pickup is a monitored by SMTP server and on creation, it send the mail to the correct destination. Also, the pickup is automatic authorized. SMTP does not have to worry about access if it finds a file in pickup directory unlike becoming a relay over TCP socket.