Hi, occ_user.
This cannot be done with a rule. Rules only fire when a message is received or after it's sent. This requires a macro. The macro is simple enough, but it will have to be deployed to every computer. Outlook does not have an automated means of distributing macros. Deploying the macro will have to be done manually. The more computers there are in the organization the more of a pain this becomes. Also, a savvy user could turn the macro off.
The above aside, here's the macro. Follow these instructions to use it.
Outlook 2007
1. Start Outlook
2. Click Tools > Macro > Visual Basic Editor
3. If not already expanded, expand Microsoft Office Outlook Objects and click on ThisOutlookSession
4. Copy the code from the Code Snippet box and paste it into the right-hand pane of Outlook's VB Editor window
5. Edit the code as needed. I included comment lines wherever something needs to or can change
6. Click the diskette icon on the toolbar to save the changes
7. Close the VB Editor
8. Click Tools > Trust Center
9. Click Macro Security
10. Set Macro Security to "Warnings for all macros"
11. Click OK
12. Close Outlook
13. Start Outlook. Outlook will display a dialog-box warning that ThisOutlookSession contains macros and asking if you want to allow them to run. Say yes.
Outlook 2003 and Earlier
1. Start Outlook
2. Click Tools > Macro > Visual Basic Editor
3. If not already expanded, expand Microsoft Office Outlook Objects and click on ThisOutlookSession
4. Copy the code from the Code Snippet box and paste it into the right-hand pane of
5. Outlook's VB Editor window
6. Edit the code as needed. I included comment lines wherever something needs to or can change
7. Click the diskette icon on the toolbar to save the changes
8. Close the VB Editor
9. Click Tools > Macro > Security
10. Set the Security Level to Medium
11. Close Outlook
12. Start Outlook
13. Outlook will display a dialog-box warning that ThisOutlookSession contains macros and asking if you want to allow them to run. Say yes.