In some cases mails send by a VB application using CDO or MAPI the ASCI attachment is lost or corrupt.
The thing is that the sender can see the mail in his sent items with the attachment but the recipient receives the mail without the attachment, or the ASCI file can't be used anymore.
In some cases this is because the winmail.dat file is send along with the message.
This is the Exchange client adding Rich text information after the ASCI file.
This can be prevented.
For more info seen
Exchange administrator can do this.
Go to Exchange System Manager. Open the Global settings container and select Internet Message Formats.
In the right pane click new domain.
Fill in the required fields. As the example below. Replace test and test.com with the appropriate domain where you want to send RTF files to.
If the value is set to Never, RTF information is never sent.
If the value is set to Always, RTF information is always sent, regardless of the recipient properties.