The issue seems to be related to the
xdg-email script, as you already pointed out. Chromium uses this script as a handler for opening mailto links. I think that for some reason your DE (Deepin) is not recognized by
xdg-email or its value is getting overwritten (?).
After searching, I found a possible solution in the Arch Forums:
https://bbs.archlinux.org/viewtopic.php?pid=1419953#p1419953 (post #4 of the thread)
This approach suggests ‘hacking’ the
xdg-email script located in the /usr/bin/ directory. This is not a very elegant solution, since this file will get overwritten when the package
xdg-utils gets upgraded to a new version, but it might work.
I tested this, using DE=“gnome3” in my system (XFCE) works as expected.
Another approach would be using
xdg-open instead of
xdg-email for opening mailto links in Chromium. First you have to confirm that
xdg-open email@example.com should open the default email client (Thunderbird in this case), just like
xdg-email firstname.lastname@example.org would.
xdg-open works, you can try out this tutorial from the Arch Forums:
Bare in mind that this is an old tutorial, so the provided information might be outdated or invalid (I didn’t test it).