<blockquote> Will the Emails that I have on my computer stay on my computer when I change the Imap address? Or will those go away? </blockquote> You'll have to download an offline copy of all your messages to your local disk prior to losing access to your Gmail account. In Thunderbird speak this is called 'Synchronization'. https://support.mozilla.org/kb/imap-synchronization With IMAP, messages are stored and manged on the server. An offline copy will allow you to still having access to your messages locally after you lost access to the old IMAP account. And you'll have to put Thunderbird in offline mode for this, otherwise it would still attempt to access the old server, and fail. Therefore downloading the entire message archive from the old server to your Local Folders account may be the more reliable method. Gmail allows to export the entire message archive, which then can be imported to Thunderbird Local Folders. Also, a backup of the entire Thunderbird profile prior to switching accounts is highly recommended. https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data#w_backing-up-a-profile Once the new account is active, don't mess with the existing account in Thunderbird. Set up a new account for the new server instead. You can then upload your existing email archive to the new server if this is what you want. <blockquote> I have three emails (aliases) Info@ Shows@ and Judy@goldenwoodsoap.com Are those treated seperately or do those get moved along with the one change? </blockquote> Since you have to set up a new account for the new server in Thunderbird nothing gets 'moved along' automatically. <blockquote> Do I keep the Port #993 is this SSL/tls and do we still use the OAuth2 authentication. </blockquote> Check with your new email provider for the required server settings.