RESOLUTION
This behavior is by design and not documented correctly in the Outlook Visual Basic Reference Help file (Vbaoutl9.chm).
If you want to populate the body of the message and still send the message in Plain Text format, you can use the Collaboration Data Objects (CDO) object model. The CDO object model sends Plain Text messages by default.
For additional information about obtaining CDO, click the article number below
to view the article in the Microsoft Knowledge Base:
171440 INFO: Where to Acquire the Collaboration Data Objects Libraries
For additional information about an example of using CDO to send a mail message, click the article numbers below
to view the articles in the Microsoft Knowledge Base:
153311 ACC: Using Automation to Send a Microsoft Exchange Message
161833 HOWTO: Send Mail from Visual Basic Using OLE Messaging
Both Outlook 2002 and Microsoft Office Outlook 2003 include a new property named
BodyFormat. In later versions of Outlook, you can use the
BodyFormat property to programmatically switch between mail formats.
REFERENCES
For additional information about available resources and answersto commonly asked questions about Outlook solutions, click the article number below
to view the article in the Microsoft Knowledge Base:
146636 OL2000: Questions About Custom Forms and Outlook Solutions