If you want to send an email to a contact person on a client side, you must first integrate your inbox with Traffit. HERE there is the instruction on how to do it. 

If you already have an inbox, go to CRM -> Clients-> Choose a specific client.
Click on the 3 dots next to the contact person. There you find the option "send message".
The message writing window will open. You can either write the message by hand or use a ready-made template.