The message resides in the delivery queue in the active state but no delivery attempt is made when the delivery binding for that route is set to "Auto".
This is a known issue with using AUTO for the delivery MTA's interface binding and was addressed with SMG 10.6.0-5.
Workaround with SMG 10.6.0-3
Change the Scanner -> SMTP settings -> Advanced settings -> Delivery -> SMTP delivery bindings from AUTO and select one of the available network interfaces to use for the delivery binding.