How to Get Mail Back After Failed Migration To New Computer

This may be off topic, but I’m hoping someone may know the answer.

I just migrated from a 2015 iMac running Mojave to a new 2019 iMac. For some reason the migration assistant didn’t fully copy everything over, and as far as I can tell it looks like Movies, Music, Photos, and some mail files. I’m sure there is more.

In Mail, it looks like all of my mailboxes are there, and they have picked up the last 30 days of email from the server. But I am missing the user created mailboxes you can create that look like folders. I have stored a huge number of emails in there over the years, including tax receipts, password emails, etc.

I went to ~/Library/Mail/V6 on the old machine and copied the folders there and copied them to the new machine, but nothing showed up.

Does anyone know where these user created “folder” mailboxes are stored, for lack of a better term?

Also, I had coped some of my emails to DevonThink awhile back, but have not kept up with it. What would be the best way to back up mainly those user mailboxes once I get them back.

Your 2015 iMac should be untouched by Migration Assistant. Are the files still there?

Yes everything is still on the old iMac. I have copied most of what I think I am missing onto a USB drive and have imported in most of it. The emails are what don’t seem to be working correctly. I copied the contents of the V6 folder but the mailboxes I mentioned did not show up.

It looks like I have solved this. I copied everything over again, restarted again, and for some reason the mail folders appeared. Not sure what it was nor if everything is there, but it looks hopeful.