You can't send an email to one customer through Hakema. but you can invite a customer to your Booking Page.
Also in Hakema you can your default email program (like Gmail or Outlook) from the customer profile to send email. To do so:
On the Customers Page, go to Search function and find a customer by name. (see Finding a customer)
Click on the customer’s email address. (see below)
An email draft will open in your default email program.