transferring from thunderbird to apple mail

I don’t use TB. However, I consider you possibly can export e mail in MBOX format which Apple Mail can import. First, if you’re utilizing IMAP protocol to join to your e mail service then you definately shouldn’t have to export/import something. With IMAP, all of your messages needs to be saved on the e-mail server. Simply arrange your account in Apple Mail and your messages will load. Since Apple Mail is loading e mail messages, it can load the e-mail addresses within the messages. vCard file can probably be imported into Contacts app.