Duplicated mailheaders when sending from system.net.mail.smtpclien

Hi,
When I send mail from a c#-program using SmtpClient in System.Net.Mail some
of the information in the mail-header is duplicated. The result is that some
receivers does not receive my email because it does not meet the rfc-standard.
The information that is duplicated is: "Mime-Version 1.0", "To", "From",
"Date" and "Subject". The duplicated fieldnames are all in lower-case.

The SmtpServer in use is located on one xp-2003-server, when I run the
program from my local pc the headers are not duplicated, but when I run the
program from some other xp-2003-servers the headers are duplicated. I have
noticed that the version of inetifo.exe are different on all servers
including my local pc.

Does anyone have any idea why this happens ?
regards
Kvitepus