Interesting behavior… In this case you sent the topic and it did arrive well, but to the wrong category: it arrived in the mailinglist mirror.
Basically the mailing list mirroring is done in discourse is it filters anything sent to the qubes-users@googlegroup… to that category. Because you had both addresses it went into that one instead of the general category.
So a way to go around that may be to send one email to the mailing list and then resend exclusively to the forum address. It’s a bit of an extra effort. Sorry about that.
If you get some error because (at least created manually) one cannot create two topics with the same name. Then just change the title a tiny bit. Idk.
Sorry about this. Trying to harmonize email users and forum user’s experiences is an ever-improving process…
This is the unlikely combination of two niche features of discourse playing: the new topics by email and the mailing list. Although individually they are not terribly supported, my guess is the combination of both features is so rare… Regardless, I’ve asked on the discourse meta forum if there is any solution.