I am using WWipstuff.dll to automate sending email. One of our recipients, "EasyLink Services", rejects the mail for this reason:
*------------------------------------
Your request .... with a subject of /WWImport test, attached plain TXT file/
could not be delivered.
Your document contained an attachment that could not be processed
by our system. The reason for failure is:
File type not supported in MIME attachment: text ; charset =
"iso-8859-1"
*----------------------------------------------------------------
Actually it does not matter what file is attached: I test it with DOC and RTF with the very same result.

The strange thing is that I am able to send the very same message and attachment manually from MS Outlook without any problem.

What should be done to avoid the failure?