You can’t. This has been asked and answered on the forums already. Please use the available search function.
But here is the answer again…
Apple deprecated Apple Mail plugins and broke things for all third-parties who develop (and also sell) these plugins. There is nothing we can do about this. Their mail extensions, are (1) very basic and limited, not capable of providing the functionality of our plugin, and (2) have really not been further developed further or improved by Apple in the 4-5 years since they announced them. Logically, mail extensions have not been adopted by most developers and now Apple has left them – us included – with no functional replacement.
Alternative methods for importing emails into DEVONthink:
- Drag and drop from many (though not all) email clients: to the Finder and into DEVONthink, into the Sorter, or into a database directly
- Mail scripts in scriptable email clients
- Mail rule scripts in Apple Mail
- DEVONthink’s View > Import sidebar still works, albeit more slowly without the plugin
- You can also export mailboxes to .MBOX format is some email clients. The exported .MBOX files can be dropped onto DEVONthink’s dock icon to be imported.
Also make sure DEVONthink has Full Disk Access and its Automation requests allowed in System Settings > Privacy & Security.