There may be options here. Some hosting companies offer to do 100% transfer of the entire account when doing setup. I suggest a first approach would be to discuss the specifics of that with the new host, especially the email accounts. That would give you everything. Many hosts also allow a staging review so you can see the contents of the transfer prior to switching domain name to new host. That would give you the assurance you want and would require few changes changes in thunderbird, primarily the server setup to whatever the host specifies. Doing that may require using a more costly hosting company, but I encourage investigating this approach. Or, you can move the account's email yourself: Your email messages are stored on the hosting servers. Should you switch to another host, the messages would need to be moved. The safe way to do that has multiple steps - and can still have problems, not because of Thunderbird but because IMAP was designed for downloading messages, not uploading. Here are sample steps: # check at account's synchronization&storage settings to verify that all desired folders can be downloaded # then, click file>offline>download to ensure that you get all headers and content downloaded # install the addon, importexporttools, if not already done # highlight an account folder to transfer, such as inbox, rightclick, select importexporttool to export mbox - repeat for all folders # now, reverse the process: highlight Local Folders, rightclick, select the importexporttools option to import mbox - repeat for all folders # at this point, you have all the messages local to PC. For safety, I suggest backing up the profile at this point. # now, set up accounts on the new host # to upload the messages, I suggest creating a manual filter for the upload, as that automatically applies a slight delay on the process and increases the probability of uploading all messages intact. Afterwards, do a spot check.