Question:

My agents have set up ‘Out of Office’ automatic replies on the email accounts which have been setup in their agent profiles, but the users are not receiving the reply notifying them the agent is away.

Answer:

This is actually designed behaviour. The email notifications that are sent to the agent trigger the OoO reply to be sent to the helpdesk, which is then automatically rejected due to being recognised as an ‘agent_bounce’:

Instead, when your agents are away on holiday you could set up a a trigger to send the user a reply that the previous assigned agent is away, and to either un-assign or reassign the ticket