I do this set of keys which if am reading above correctly is what you want
Settings > Files > Emails, you can now define a hotkey for importing a mailbox or selected emails in Apple Mail and Microsoft Outlook*. For those who previously used the plugin, set them to ⌃⌥⌘M for messages and ⇧⌃⌥⌘M for mailboxes and it will feel like it did before.
+1, It would be great to see more development resources allocated to the mail archiving side.
Very slow reply to this, but I finally got round to troubleshooting my issue this morning and the short answer to your questions are: no 
There are no scripts running (though I appreciate the belief in my ability to set one up!) and although the log is flagging that there is a duplicate, no such duplicate exists (I checked properties and there are 0, and I ran a search on subject line to see what files might come up).
I bring in emails into my database via drag and drop from the Mail app, and did wonder if the warning of a duplicate email is being caused by the Mail app being visible in the import sidebar on DT. I don’t need it in there (and don’t know if I am the one that put it there). I couldn’t see a way to remove it, is that possible?
To be honest it’s not the end of the world if I keep getting the error message. I’ve had it for months and I know it’s incorrect (as does DT given that it’s still importing my emails) so it’s not really inconveniencing me!
It’s not necessarily a duplicate but could also be existing email with the same message ID in the database.
How would I check if that were the case? It seems unlikely (I assume message IDs are unique? The email is only being brought into the db once. And although DT is reporting that it’s skipping the import of a duplicated email, it isn’t skipping it.)
They should be. Unfortunately they aren’t always, especially in case of e.g. old emails sent by buggy software or mailing lists. A screenshot of the logged messages would be useful.
Here’s a screenshot. It does it for every email I import though so I’m not sure how helpful this screenshot is! (I drag and drop the emails I want to save from Mail to the relevant group in my database.)
Seems there’s indeed already an email with the same message ID in the database.
Yes, but that’s my point. There isn’t. I’m getting this error for every email, and the emails are only imported into DT manually by me. Unless we think none of the emails I archive have unique IDs, DT has an issue somewhere. (But I do still wonder if it’s something to do with that import sidebar.)
Are you able to import them to a new database? All of them?
Fun question! I set up a new database and tried moving some new emails into it, and I get the same error message.
In DEVONthink, hold the Option key and select Help > Report Bug.
I have this problem too. 4.1.1. Sequoia.
DnD from Apple Mail fails, even single mails, with Devonthink claiming that the mails have already been imported. Only restarting Devonthink with no databases and creating a fresh database seems to get the emails in.
Airmail, which Devonthink will only take one email at a time from, does import almost correctly, but I have to run a script afterwards to correct the mtime back to the email date.
Are you sure the emails were not already imported to the same database or are still in the trash?
One set of emails was in the trash (trashed from a different open database). The second set failed on the first import (I think one email was imported from 29), but attempting to reimport failed because Devonthink claimed all 29 had been imported.
The number of imported and failed messages is logged to Window > Log.
Indeed, that is what I was watching in real time.
A screenshot of the message(s) after trying to import some emails to a new database would be useful, thanks.
Very slow reply, but I did some email filing yesterday and watched the whole time, and none of emails triggered the duplicate warning, so it looks like something in a recent update has fixed this! Thank you!
