Re-enabling a disabled add-in
Here are the steps to enable a disabled plugin on Outlook 2013/2016:
1) Click on File > Info > and select "Slow and Disabled add-ins":
2) Enable Redmine for Outlook:
Click on Enable this add-in.
Button Enable will change to Disable, the add-in will be
loaded.
Here are the steps to enable a disabled plugin on Outlook 2010:
Click on the "File" tab in your navigation and Click Add-in:
Click on Enable this add-in.
Button Enable will change to Disable, the add-in will be loaded.