In September 2015 Google introduced a new way of remarketing to already existing customers by way of uploaded email addresses.
This feature, called Customer Match, is described at https://support.google.com/adwords/answer/6276125?hl=en.
You find it under Shared Library / Audiences / +Remarketing List, see image below.
You upload a list of email addresses of customers for targeting them with ads while they are logged in and searching on Google, in GMail, or YouTube.
Targeting existing customers in essence tries to convince the same people to spend more money with you, as opposed to finding new customers.
Some useful scenarios for configuring the targeting criteria of Customer Match are:
- terms related to the customer’s original transaction for cross selling
- terms of the customers original transaction for repeat selling
- searches for competitor names and products as a friendly reminder that you are also open for business and ready for the competition
- high performing keywords for your business
Google has extensive privacy protection measures of the uploaded emails, e.g. emails are hashed so they cannot be stolen during transmission.
In summary, Customer Match is yet another channel of Remarketing thanks to Google’s ubiquity.