Correct. If the user is not on Exchange, there is no direct way to change
the sender for an outgoing message. These are known (and sometimes partial)
workarounds using native Outlook functionality:
1) If the user has Outlook 2002/3 and is not using WordMail as the editor,
you set the sending account using CommandBars techniques. See
http://www.outlookcode.com/codedetail.aspx?id=889 for sample code.
2) You can set the SentOnBehalfOfName property, but the recipient will
probably see the user's default sending address as well, which may not be
desireable.
3) If you're mainly concerned about replies to your message going to the
correct place, add the desired reply address to the MailItem.ReplyRecipients
collection.
The third-party Redemption (
http://www.dimastr.com/redemption/ ) library
adds two other solutions:
4) Set an RFC822 header property, as described at
http://www.dimastr.com/redemption/faq.htm#14
5) Set the RDOMail.Account property, as described at
http://www.dimastr.com/redemption/rdo/RDOMail.htm
--
Sue Mosher, Outlook MVP
Author of Microsoft Outlook 2007 Programming:
Jumpstart for Power Users and Administrators
http://www.outlookcode.com/article.aspx?id=54