It seems to be a hit or miss. A few days ago I dragged and dropped from Apple Mail into a Group in DTP, it worked with no issue.
Today I tried copying a short thread (also tried individually) and received error messages. “Import of 2 messages failed”, then “Not Connected to Internet. CK ErrorDomain 3” (yet I am connected, as I type this and read articles on the web). They might be unrelated, as the latter message keeps repeating.
I don’t want to do any bulk email processing as I’ve seen some like to do, just import a few specific emails to DTP.
I tried quitting and restarting both apps, no change.
I too have been running into this issue recently. Dragging and dropping emails straight from MacOS mail will work for a while and then stop. Haven’t worked out why.
I did the above suggested Mailbox rebuild and that didn’t seem to make any difference. (Caveat: it is a huge mailbox and I don’t see a progress bar for how long it should take so that also might still be an issue)
I moved on to @BLUEFROGs suggestion of using the Finder as a middle step on this process. It worked on some small test groups but then it too stopped working. I was able to track it down to two emails in a thread that had .txt files as attachments. Those two emails wouldn’t even show up when dragged to the desktop.
With this knowledge I went back to DT and I could drag the emails without attachments directly into DT without doing the Finder step. The ones with attachments wouldn’t work at all, to finder or DT.
Yet, sometimes it works, attachments or not.
EDIT/ADDENDUM
There’s definitely a lag in how Mail processes some messages. When I returned to the Finder folder a while after I was working on this, many copies of the emails I had tried to drag into the folder were there now. So it was working in some form BTS but with no way of knowing progress or level of success.
Apple Mail/DEVONthink almost fail (but is very slow) if there are any messages being imported into DEVONthink with a MIME part of Content-Type: text/enriched
Enriched text was an early markup system before HTML became dominant (as it was envisaged to in the enriched text RFC),.
Although the RFC is dated 1996, I was still receiving messages so encoded in 2018 (i.e. The Late Pre-Covidian Age ).
See my comments in this thread:
Yet another gotcha in data preservation and portability.
FWIW, I ended up moving those messages out of the mailboxes they were in, editing the source data to exclude the text/enriched MIME part, and then importing then. I didn’t bother converting them to HTML.
If you want to search for such messages, you can export individual Mail mailboxes to .mbox format, then use a text editor to search that file for the Content-Type: text/enriched string.
Feel free to reply or PM if you have any questions, I’m Replying here for posterity
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