Try this: # delete the invalid addresses for a fresh start # enter one good email address with fields you normally use into thunderbird' addressbook # click the three dots to the right of addressbook name and export in csv format. This will be your template # open that export into a spreadsheet program # note the top row. this shows the columns as thunderbird expects them to be # open your exported outlook csv into spreadsheet and adjust columns to match, including the top row. # save as csv # import into thunderbird Note: the import process does allow for manually adjusting columns during the import, but this is easier.