Your main problem is that you can't do exactly what you want to do. A Mailing List is a subset of an address book, so formally speaking, you would import the addresses into an address book then create the Mailing List within that address book. I can suggest two methods 1) Save the relevant columns of the Excel spreadsheet to a CSV file and import that. Thunderbird's Address Book has tools to import various text files, including CSV. Doing this would require that you create a new address book within the Address Book. You may need to take steps to ensure that the CSV file is written as a utf file. Having done this, you'll still have to add the imported contacts to the Mailing List. 2) Create if necessary then open a Mailing List for editing. Select and copy the list of addresses from your spreadsheet and simply paste them into the open Mailing List's editor. Doing this should add the pasted addresses both to the open Mailing List and to the host address book. I think the choice between these two approaches comes down to whether you want to add the imported contacts to an existing address book, or create a new address book for them. The CSV route will allow you to import additional data such as street addresses and phone numbers, but this doesn't appear to be one of your requirements. And do they need to be in a Mailing List rather than in an address book?