Merging mail imports

Hello, I have a specific Mail (and notes) database (I’ll call ‘A’) from a couple of years back. In cleaning up some other databases I found that, for some reason I don’t recall, another database has a group of emls also from an import (‘B’).

The database ‘A’ is arranged where mailboxes are groups and mail threads are in some special groups (little conversation icons). Those groups don’t exist in ‘B’. I’d like to merge ‘B’ into ‘A’ but I don’t want to botch things up. There is duplication, but I don’t know how much out of the thousands of emails.

Basically I’d like one mail database that is ordered if that’s possible. What’s the best approach here? I don’t know anything about the eml structure, whether it has hierarchical info of being part of a thread. If I just drag and drop is there a way to straighten things out?

If some of the databases are definitely identical (including the internal identifier), then moving them from one database to the other should create a replicant, not a duplicate, in the latest versions.

Indeed! Just for posterity I want to note that it seemed to work for my case. I just did a simple drag and drop and got huge list of “UUID already exists in database” log entries. So I guess there is a check across the whole database which I didn’t expect. cool. Thanks