2.Setup your Gmail account in Thunderbird: Select File -> New -> Existing Mail Account
3. Enter your Gmail-account details and then choose Continue
4. Select POP3 and then Done (The settings should be generated automatically).
5. Copy the email and folders you want Select the emails you want to import from you Gmail-account. Then right click and either choose "Move To" or "Copy To" (in this case there is no difference). Then select your Countermail-account and then select which folder you want to import to.