Do you use a Pop or IMAP mail account? re 'did a full back up of all my email and address book.' How did you do this? Did you use 'Mozbackup' tool to copy the entire profile or did you export the emails as .eml files using ImportExporttool addon or manually save as .eml files? Or did you manually access the Profile folder, then the Mail folder, then the mail account name and then copied all of those files? Please explain. Did you export the Address books or access the profile folder and copy the .mab files? Are you talking about 'Personal Address Book' and 'Collected Addresses' or others you created? Currently, what do you see? Can you only see the imported old stuff or only the new emails? How many Profiles do you have in the Profiles folder? Do you have more than one? A default profile name will have letters and numbers eg: abc1d234.default and usually located here: C:\Users\UserName\AppData\Roaming\Thunderbird\Profiles\ How to move to a new PC: http://kb.mozillazine.org/Move_to_a_new_PC If you have one Profile and the only emails you see are the new emails, then Use ImportExport tool addon to save/backup those emails as .eml files and save them in new folder on the desktop. ImportExporttool: https://freeshell.de//~kaosmos/mboximport-en.html Then on old computer install Mozbackup tool and use it to backup the entire Profile. * Info on backup: http://kb.mozillazine.org/Profile_backup * Info on MozBackup tool: http://kb.mozillazine.org/MozBackup * Mozbackup tool: http://mozbackup.jasnapaka.com/ copy the *.pcv file to desktop on new computer. Install Mozbackup on new computer and use to restore the old Profile onto new computer. Then use ImportExporttool to get the saved .eml files back into Thunderbird. re: address Books: http://kb.mozillazine.org/Moving_address_books_between_profiles The MozBackup tool should move the default address books, but other address books may need to be exported as either LDIF files or .csv files and then Imported into new Profile on new computer.