re : I have therefore deleted the old account. Are you talking about a POP or IMAP account? '''If imap,''' I would immediately try to recreate it in the hope you still can access the server. This time make sure the folders are set up to fully synchronise and download full copies and not just headers. https://support.mozilla.org/en-US/kb/imap-synchronization#w_configuring-synchronization-and-disk-space-usage Then File > Offline > download/sync now Select 'Mail Messages' and 'Work offline once download.....etc' The select button will show you what folders are selected - note that subfolders would need to be selected. click on OK In offline mode, select emails and use right click and 'Copy to' and select a folder in 'Local Folders' account to get the copy off the server and onto your computer (Later you can copy them back onto a different server.) OR if transfering to a POP account, you can directly copy them into pop account folders.