Your guess is correct. The safest way to do it is first to create a folder under the Local Folders account. You could have one folder if you want to keep all the messages together, or more than one if you want incoming and outgoing messages kept separate. Then highlight and copy the messages from the inbox and sent folders for the defunct account. When you are happy that all have transferred safely you can delete them from the inbox and sent folders. That's the safest way, as I say. You '''can''' just highlight and drag them, you can even drag whole folders, but then people sometimes report that messages go missing so I err on the side of caution. Remember that once messages are in Local Folders there is no backup for them on a server. So you need to keep a safe backup copy of your Thunderbird profile. (Good practice anyway.) To stop Thunderbird polling the server, go to Account Settings > Server Settings and untick the relevant boxes.