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Migrating the address book
The address book won't be automatically transferred. You find the address book in C:\Program Files\Courier Email\Mailbox\Courex
To import it properly open Thunderbird, go to address book/tools/import. Choose the text file option in the next window. In the 'select address book file' window change the 'Files of type' to 'All Files'. Then choose 'Address.csv' .