Thunderbird Duplicate Contact Manager

Martin Brinkmann
Dec 18, 2007
Updated • Jun 26, 2017
Email, Thunderbird

I reviewed a Thunderbird extension to remove mails yesterday. Today, I'm going to review an extension that finds duplicate contacts in the address book of the email client instead.

The add-on handles one address book currently which is a little unfortunate but the author promises to integrate functionality that enables you to check all address book instead. So, you can only search for duplicates in a single address book, and not in all of them.

Duplicate entries can appear in several different ways. A common one is a corrupt address book file for instance, but it can also happen when someone sends you emails from different mail accounts.

Duplicate Contact Manager

find manage duplicates

You can use the Duplicate Contact Manager to merge those information by adding the second email address to the first address book entry, and by deleting the second record afterwards so that only one entry remains containing all the data.

The add-on window can be launched by opening the address book in Thunderbird and clicking on the - newly added - Duplicates menu and there on the Find and manage Duplicates entry.

The process takes a while and is semi-automatic. There is no information how the extension compares the address book entries but my understanding is that it compares several parameters such as the display name, first and second name, or email address, and displays those entries if it finds a match.

This does mean however that you will get lots of matches for popular first names such as John or Mary. Takes a while as well depending on the amount of contacts in your address book.

The program works with contact pairs only. What this means is that it will always displayed a first and second contact set next to each other that it believes to be duplicate.

You can skip any if you come to the conclusion that it is not a duplicate, or merge the two sets right away instead. Here you can select to keep the first or second contact before you hit the apply and continue button.


Duplicate Contact Manager is a useful extension for the Thunderbird email client. While there is no need to run the extension constantly, you may want to run it whenever you discover duplicate contact entries in one of your address books.

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Duplicate Contacts Manager
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