Works good, figured out
This did the trick
Open your Thunderbird program and go to “File > New > Existing Mail Account”
Enter your details including the email password and tick “Remember password”, then click “Continue”
Click “Manual Config” or wait until the automatic scan fails
Enter the connection details:
Incoming mail server: choose IMAP and enter your server name in format terrassl.net
Outgoing mail server: repeat the same entry as for incoming
Enter the full email address as username
Set encryption to “SSL/TLS”
Set Authentication to “Normal password”
Click “Done” it should start to import mails if everything is correct