A fun Thunderbird extension that I installed a couple of days ago is the Display Mail User Agent Extension. This extension looks at the X-Mailer header in mail and displays the icon for the email program that was used to create the email. So now I can easily see which mail programs are used by people who write to me. Which is interesting, but hardly useful.
Of course it only knows about a certain set of programs. But I’m impressed by its breadth of coverage. Today I saw the Perl camel symbol appear next to an email. On further investigation I discovered that the email was created by someone using the Perl MIME-Tools package. So there’s a nice subtle piece of Perl advocacy.