The.com is a streamlined system and our continued goal is to make every piece of the website process easy.
Because of that we only connect domain names via CNAME records. That way the registrar (like GoDaddy, Namecheap, Name.com, etc) stays in control of all the rest including email.
Inside your registrar, you will set your MX records to whatever email service you have set up (we recommend Gsuite)
Here are a few helpful links for connecting Gsuite to your registrar: