- Quit Mail.
- Quit DEVONthink 3.
- Enable Full disk access in System Preferences > Security & Privacy for DEVONthink 3
- In the Finder, hold the Option key and choose Go > Library .
- Go into the Mail/Bundles folder and delete the DEVONthink.mailbundle .
- Relaunch DEVONthink 3 and install the Mail plugin from the DEVONthink 3 > Install Add-Ons .
- Relaunch Mail and enable the plugin via Apple Mail’s Preferences > General > Manage Plug-ins .
Note: You shouldn’t be running 2 and 3 simultaneously.