Ok, I opened up Mail and it prompted me to create an account. I tried to not create one and just hoped it would open the application, but nada. I then created a dummy account and went into the Import wizard. I identified the Thunderbird tree from the W7 computer copied to a USB flash drive, but the import only brought in the messages and folders. Seems like Mail cannot import account settings. Before laboring the point of re-creating the individual mailboxes in Mail, I'll install Thunderbird for Mac and see if it can install from Thunderbird for Windows.