I also encountered this bug. It affects any program that passes attachments to Thunderbird (I hit it while using DarkTable 1.1 under Ubuntu 12.10 Quantal Quetzal). See attached patch for a simple fix.
Note that there is a newer version of xdg-utils included in Debian, but it contains other bugs. ** Patch added: "xdg-email.patch" https://bugs.launchpad.net/ubuntu/+source/xdg-utils/+bug/1019259/+attachment/3457022/+files/xdg-email.patch -- You received this bug notification because you are a member of Desktop Packages, which is subscribed to xdg-utils in Ubuntu. https://bugs.launchpad.net/bugs/1019259 Title: xdg-email fails to launch Thunderbird Status in “xdg-utils” package in Ubuntu: Confirmed Bug description: When clicking "mailto:" links in Chromium, nothing happens. I have Googled around and found that Chromium uses xdg-email for these. I think the problems is the routine "desktop_file_to_binary" which returns empty because the grep for Exec finds three such lines in the file /usr/share/applications/thunderbird.desktop. ProblemType: Bug DistroRelease: Ubuntu 12.04 Package: xdg-utils 1.1.0~rc1-2ubuntu6 ProcVersionSignature: Ubuntu 3.2.0-26.41-generic 3.2.19 Uname: Linux 3.2.0-26-generic x86_64 ApportVersion: 2.0.1-0ubuntu8 Architecture: amd64 Date: Fri Jun 29 13:10:56 2012 Dependencies: InstallationMedia: Lubuntu 12.04 "Precise Pangolin" - Release amd64 (20120423) PackageArchitecture: all ProcEnviron: LANGUAGE=en_GB:en TERM=xterm PATH=(custom, user) LANG=en_GB.UTF-8 SHELL=/bin/bash SourcePackage: xdg-utils UpgradeStatus: No upgrade log present (probably fresh install) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/xdg-utils/+bug/1019259/+subscriptions -- Mailing list: https://launchpad.net/~desktop-packages Post to : desktop-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~desktop-packages More help : https://help.launchpad.net/ListHelp