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Courier email box (if in standard location): C:\Program Files\Courier Email\Mailbox
Thunderbird : C:\Documents and Settings\....(1)\Application Data\Thunderbird #(1) here is the name of your user
The Locales folder: C:\Documents and Settings\....(1)\Application Data\Thunderbird\Profiles\qvu1n3nv.default(2)\Mail\Local Folders\ # (1) here is the name of your user # (2) this entry is similar but never the same
After the migration find a folder called Courex in C:\Program Files\Courier Email\Mailbox which contains the address box, the mailbox data (all settings inclusive passwords!) and log files.
After the migration find a folder called Courex in C:\Documents and Settings\kiwi....(1)\Application Data\Thunderbird\Profiles\qvu1n3nv.default(2)\Mail\Local Folders\ . In this folder all main and sub-folders, emails and attachments are stored.
#(1) here is the name of your user
# (2) this entry is similar but never the same