This issue was fixed in upstream bug report: https://bugzilla.mozilla.org/show_bug.cgi?id=261559 which is showing "VERIFIED FIXED" since 2008-08-07 but no target release given. Thunderbird will only register itself to handle .eml files when set as the default mail client. Tested ok with Thunderbird 60.4 in Ubuntu 18.04. No activity here for over 8 years so closing as fixed.
** Bug watch added: Mozilla Bugzilla #261559 https://bugzilla.mozilla.org/show_bug.cgi?id=261559 ** Changed in: thunderbird (Ubuntu) Status: Triaged => Fix Released -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/196887 Title: Missing file association for Thunderbird To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/thunderbird/+bug/196887/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs