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Clacks Overhead 1.0.1
In tribute to the late Sir Terry Pratchett, many users are adding the message "GNU Terry Pratchett" into the email header "X-Clacks-Overhead". Clacks Overhead shows users when this appears in their emails and displays the message included.
About this Add-on
GitHub repository: https://github.com/Bhyn/Thunderbird-Clacks-Overhead