On Macbook pro computer: * Exit Thunderbird. * Access the profile folders on MacBook Pro. ~/Library/Thunderbird/Profiles/<Profile name>/ * 'Mail' folder will have pop mail accounts and 'Local Folders' mail account. * 'ImapMail' will contain imap mail accounts. Within Pop, Imap and 'Local Folders' mail accounts, emails are stored in mbox files. mbox files do not have any extension and have same name as the folders you would normally see in the Folder Pane. Any file with .msf extension is just an indexing file and hold no emails. Any folder with a .sbd extension means you had subfolders, so those .sbd folders may also contain mbox files. * Copy all the mbox files and put them onto a usb or external hardrive. * On imac computer, exit Thunderbird, access the profile name folder. * Click on 'Mail' folder * click on 'Local Folders' folder. * copy and paste the mbox files on usb/external hardrive into 'Local Folders' folder. * Start Thunderbird. You could just leave all the emails in the Local Folders mail account. If you need to get those emails back into an imap account in order to put back on server, you can copy and paste them into an imap folder. But do it in small batches as folders will need to synchronise each email, which is a load of gibber jabber between Thunderbird and server. But this will use up quota space on server.