Ongoing email import


I’ve recently upgraded to DT Pro Office (v2.3), but am struggling to understand how it handles email.
When I import email from Apple Mail, it imports threads. Great!
However, after the initial import, I am using Mail rules with the DT plugin to add all incoming mail to DT. However, this doesn’t then find the threads for those email that are coming in.
If I try to manually import, I’ll get replicates of the email that has already been sent it by the plugin.

I suspect I’m missing something fairly rudimentary, but could someone please help me understand how to manage incoming email?