Hi There are a few options. Bear in mind if you are using IMAP you may not have all the messages in full on your computer in Thunderbird. IMAP downloads the message when you open it. If you are using POP, the whole message is downloaded already. So for IMAP you may need to perform extra steps to download everything before deleting or disabling the account. Then - If you do not intend to use Thunderbird to access any other email accounts - you might set Thunderbird to offline. Then just remember not to change the setting to online. Options - Advanced - Network & Disk space - set to manual state offline. Or - you might set specific folders to be offline folders. http://kb.mozillazine.org/Offline_folders (this article may not be up to date) Or - you might copy/move/drag and drop all the emails you want to keep to the "Local Folders" directory structure which saves them locally. Then set up the new account and delete the old account. http://kb.mozillazine.org/Local_Folders I am not a Mac user, so not sure I can give you complete guidance - the Thunderbird options sometimes differ between operating systems. Hope that helps.