The easiest way to check if a contact received a particular email, is to check their timeline.

A contact timeline contains a visual record of all communications sent to and opened by the contact, as well as all clicks on properties from your ActivePipe emails. 

You can access a contacts timeline through the Contacts menu. From here:

• Click on the Contact List tab.
• Search for the contacts name, email, or CRM ID using the magnifying glass found top right of your screen.
  
• Click on the contact to be taken to their Contact Profile.
• Click on the Timeline tab.
• You can filter down the date range, as well as by sends, opens or clicks to help locate what you're looking for.

Scroll down the timeline to see if the email you are looking for appears.