Zendesk should create a side panel that opens automatically that shows all tickets associated with the email within the selected ticket. I saw this in another help desk system where when the customer writes in, all their previous/additional tickets associated with that email address or another email address that is part of the profile populate in a side panel for the agent.
An example is when an agent is working on a ticket for a customer that has submitted multiple tickets about different subject the same day, all show in the side panel along with other tickets associated with the email address. Agent is able to work on multiple issues instead of addressing the one issue they see because they may forget to click the profile to check for other issues.
This is critical for our business as our agents do sometimes forget to check and this results in multiple responses from multiple agents which could have been handled in one interaction. This can also result in unsatifsactory customer reviews due to the missed opportunity.