There are two ways to create a customer through the Merchant Mail Gmail add-on.
Creating a customer when one does not exist for an email
Merchant Mail automatically looks up Shopify customers based on the sender of the email you are reading. If there are no customers with a matching email address, you'll be given the option to create a new customer.
Click on Create Customer and enter the customer details. We automatically fill in the name and address based on the email you are reading.
Click the Save button to create a new Shopify customer.
Note: If you wish to send account invite emails (also known as account activation emails) when creating a customer, then you must enable account invites through the settings menu. Once that is done, you'll see an extra option when creating customers.
Creating a customer through the More Actions menu
You can also create a customer at any time, though the More Actions menu.