There seems to be no difference in these headers between the old and new emails, except for the fact that the old From headers include the via statement.
(For context my site name is Collectives, my old domain was minecraftengineering.org and the new domain is saen.dev).
Everything was switched over except the notification email, which I didn’t change until a few days ago (I still own the old domain).
Old
From: Saen via Collectives <noreply@minecraftengineering.org>
New
From: Saen <noreply@saen.dev>
(Didn’t Change)
Reply-To: Collectives <incoming + [replykey] @saen.dev>Subject: [My Topic Title]X-Discourse-Sender: Saen
Maybe it’s related to the fact that I previously had different domains in use for the notification and reply emails, and now I have the same domain across both. Perhaps this triggers something in the clients that the “via” is no longer necessary?