Note: The Email Sync feature is one of the many useful features of Pipedrive’s Gold plan. To learn how to switch plans, click here.
If you add the 'last email sent' column to a list in the List View, it may remain blank (or not update) even after you send emails. This is because this field only updates according to the full email sync offered with Pipedrive's Gold Plan. If you're using Smart BCC, the emails won't be counted in this field.
In order to better to track your emails, Pipedrive Gold is the best way to go!