Manually migrating email to new Mac

I recently erased my hard drive and reinstalled macOS High Sierra.  I had previously made a Time Machine backup and wanted to bring in my old email into Mail.app.  In prior versions of macOS, I just had to copy the Mail folder into ~/Library, but that did not work in High Sierra.  Mail told me that it could not convert my mail to the new format.

I then tried the import option and pointed to the specific mailbox in Time Machine, but that made all kinds of subfolders that were difficult to deal with.  Finally, I decided to copy all the .emlx files to the same folder, rename the folder with an .mbox extension and try importing them.

Yeah!  This worked very well.  In terminal, I navigated to the Time Machine folder for ~/Library/Mail and then drilled down until I got to the Data directory of the mailbox with the messages I wanted.

Then I ran the following command to copy them to a folder on my desktop called mailbox.mbox:

find . -name '*.emlx' -exec cp -r '{}' '/Users/josh/Desktop/mail' ';'

Then I used Mail's import mailboxes feature and chose Apple Mail to import my mailbox.mbox folder.  It worked perfectly.  Now I have one Mailbox in the sidebar in Mail that contains all those messages.