Staff in Support Departments should retain emails for 7 years, or however long required by law.
Staff in all other departments, especially those that handle client data, should periodically remove emails older than 2 years.
To delete all emails prior to January 1st 2017, do the following:
1.Search your email for: before:2017/01/01
2.Select: All items on the page
3.Select: All items that match this search
4.Select: The delete icon
Screenshots included below
Steps 2 - 4