I set up an email channel in a standard JSM space. 
Full setup/workflow is thus:
Email sent to a shared email box (sharedbox@abc.com)
Mailflow rules in Exchange prepend a prefix to the email subject line "[XYZ] " then redirects the email to the wrkhubagent@abc.com account (which is the one I have set up as the email channel into the JSM space) and also redirects a copy into the original shared email box
The mailflow rule works perfectly, and the email ends up in both boxes as expected every time, no matter who sends the email
But the ingestion into the JSM space only seems to work for me and my counter part internally. Anyone else internally that sends an email to the shared email box, the mail flow rule prepends the prefix and redirects, but then NOTHING happens in the JSM space at all. No errors reported, nothing.
How do I troubleshoot this?