The Pool Dashboard is where service teams receiving tickets frequently will find many yet-to-be-assigned tickets. These unassigned tickets are can then be assigned to team members in a first-in-first-out manner. So, the ticket that has been in the queue for the longest time gets assigned first.
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For example, consider a team that has 2 members (A and B) and both have an Individual Maxcount of 5.
At the moment, both have 5 open tickets in their individual buckets, and therefore, all the incoming tickets will be held in the pool until one of them resolves/closes one or more of their tickets. Now, there is an incoming high priority ticket, this feature enables the admin to exercise their judgement, and assign the 6th ticket to either A or B as they deem fit. This manual assignment will also override the first-in-first-out concept of ticket assignment.