RE: Record Creation and Update Rule
Further investigation into this topic has determined that it is the process of having an active automatic record creation rule running that causes the incoming external Email to be created as an inactive Queue Item. Deactivating the rule allows the Email Queue Item to enter the target Queue as an active Queue Item.
So, as long as there is no requirement to create a record (ie a Case) on the back of the incoming external Email, then it works fine. In my scenario, I am trying to set up a Customer Services Queue that deals principally in processing incoming external Email. The Queue Operatives will manually (or semi-manually using a workflow) create a Case where required. The Queue will still receive CRM derived Queue Items such as Tasks, Cases, internal Email and assigned Phone Call items.
The issue now is moving the Email Queue Item out of the Queue, once it has been replied to or forwarded. As with other activity types, the Email Queue Item does not automatically disappear from the Queue once it has been processed, the Email Queue Item has to be set to inactive. A simple on-demand workflow solves this by getting the Queue Operative to select the Queue Item Details option on the main menu, for the selected Email Queue Item, and running the on-demand workflow to set the Queue Item status to Inactive. Refresh the Queue Item view and the Email Queue Item has now disappeared.
For those looking for a similar sort of queue operation, where the queue principally manages incoming email traffic, I hope this information saves you a bit of time in trying to get the auto record creation rule to work on this type of operation.