Within the latest release (v1.3.419), a bug has surfaced where emails leading to a Forward Outcome are not being removed from the Mailbox. Consequently, they are being repetitively processed, eventually causing the Mail Handler to be blocked.
If you encounter this bug, the only way to unblock your Mail Handler is to access the relevant Mailbox and deleting the problem email. Once this is deleted you will then be able to go to JEMHC > Messaging > Message Handlers and press “Release” to unblock the Mail Handler.
We are currently investigating this. We update this blog when a fix has been made.