how do I force Outlook to invoke Excel to view attachments with a certain file extension (e.g. file9.xyz)?

Answer 1

Outlook uses the file extensions defined by Windows operating system. If you change it, then not only will Outlook launch Excel for extension ".XYZ" but also Windows. (When you double-click a filename.)

Here's how to change:

1) open Windows Explorer: Start, Programs, Accessories, Windows Explorere
2) Click Tools, choose Folder options
3) Click tab on top that is labeled "File Types"
4) Scroll down to see if ".WYZ" is registered.
5) If it is listed, click "Change" and assign MS Excel
6) If it is not listed, click "Add" and assign MS Excel

Hope this helps.

Regards,
QwertyKPH @ Yahoo®