Email Attached Excel Workbook in Outlook: Disables auto open VBmac

When E-mailing within Outlook (a "New" email) and attaching an Excel workbook
with a Visual Basic auto open macro, the auto open macro is somehow disabled.

YET: If from within Window Explorer, using the right click shortcut menu, I
send the same Excel workbook with a VB auto open macro to a mail recipient,
the workbook arrives with the VB auto open macro enabled.

Questions: 1.Why the difference. 2. How to fix it so I can E-mail it within
Outlook 3. If an Excel workbook arrives with the VB auto open disabled, how
do you re-enable it.

Setup Info: Macro security settings in both Outlook and Excel set to low,
with no effect on this behavior.