The only interesting header in a Yammer email that seems plausibly relevant is X-MS-Outlook-YammerExtensibleContentData. It claims to be a list of thread IDs but the contents are at least base64 encrypted and seem to likely be signed by some key somewhere and my interest waned in seeing if I could decode it further. If that's the trigger, it's definitely not generally useful if it only exchanges Yammer thread IDs.
I haven't seen a Viva Insights email in a few days, but I was reminded it does have a full add-on installed and I wouldn't be surprised if it was much more its add-on doing the work and it was very specific to those emails as well. (Possibly it is even the same add-on managing both.)
I haven't seen a Viva Insights email in a few days, but I was reminded it does have a full add-on installed and I wouldn't be surprised if it was much more its add-on doing the work and it was very specific to those emails as well. (Possibly it is even the same add-on managing both.)