Sometimes it happens that after a reinstallation of the Outlook Add-in, the actual toolbar does not appear in Outlook. The toolbar can however be seen as a separate toolbar under View / Toolbars. The actual cause is that previous Outlook Add-ins were still active previous to the reinstallation.

To resolve the issue, do the following:
1. within Outlook, select Tools in the menu
2. select Trust Center
3. select Add-ins
4. select Apply macro security settings to installed add-ins
5. verify that COM Add-ins is selected
6. press Go
7. if the Microsoft Dynamics NAV Synchronization Add-in is selected, deselect it
8. press OK
9. within Outlook, select Tools in the menu
10. select Trust Center
11. select Add-ins
12.  select Apply macro security settings to installed add-ins
13. verify that COM Add-ins is selected
14. press Go
15. select the Microsoft Dynamics NAV Synchronization Add-in is selected
16. press OK

The Outlook Add-in toolbar should now be visible again.