We know that when a user replies by email to a thread that was in the meantime subsequently closed, he will get a Sorry email response. All well and good.
But let’s examine the cases where the thread he is replying via email has not been exactly closed, but the topic has been redirected or whatever various other combinations moderators might do.
OK, so there he is, replying blindly to an hours old email in his Gmail etc., without knowing that indeed, if he would just have a look at the website, was now part of a whole other thread or whatever.
OK, off goes his email. But when it hits the Discourse server, what happens?
Well it doesn’t generate a Sorry email reply.
But it also doesn’t get posted anywhere.
Maybe a few weeks later the user, back on the website, swears he did mention something, but cannot find it now.
No, I don’t have an exact case. All I know is I lazily just replied to several threads I found on my email account, and most got posted, but I’m certain that one didn’t. But the threads got changed around by the moderators, so the only way to find where my email went would be to “open up the drain cover on meta.discourse.com’s mailbox, and look for items that didn’t generate a reply nor a Sorry message.”
I’m saying the easiest way to debug this would be for “root” to check all the emails that Meta.discourse.com got. Each one should have generated an action. For those where no action was generated, there should be some error log. Maybe in the error log you will see: “Could not find valid thread to append reply to. Discarding.” or something.
So to fix the bug, the email should be returned to the user, (with the body too please!), saying “We’re sorry. The thread you were replying to got altered. It would be best if you examined your post and perhaps make any adjustments you see fit, before perhaps reposting your valuable viewpoints to the new thread. Yours Truly, Discourse Software Corporation Ltd. (or, OK, local site name.)”