A lot to ask in this.
1. Yes, emails are threaded based on the from address headers and the subject within the last 30 days and are attempted to be sent back to the same agent:
https://help.mypurecloud.com/articles/about-acd-email-routing/2. If you want to find the last user involved, you could look up the Email and Subject in past email interactions (or better through the CRM) and assign the last agent as the Preferred Agent for routing using the Preferred Agent Routing in the queue:
https://help.mypurecloud.com/articles/preferred-agent-routing-behavior/3. For looking at Active users in queues, you can check for the routing status of the queue and of individual users by creating a data action the Genesys Cloud API (you will need to install the PureCloud Web Services integration) and calling that with the queue or user ID.
Hope this helps to get you where you need.
Robert
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Robert Wakefield-Carl
Avtex Solutions, LLC
Contact Center Innovation Architect
robertwc@avtex.comhttps://www.Avtex.comhttps://RobertWC.Blogspot.com------------------------------