Objective
This guide cover authentication and sending emails from a subdomain, instead of a regular main domain.
Product
Twilio SendGrid
User Account Permission/Role(s) Required
Account Administrator or Teammate with Administrator privileges
Procedure
Sending from a subdomain is similar to sending from the root domain. In order to send from "@ANYdomain.com", you would need to first authenticate "ANYdomain.com" using the regular SendGrid's Domain Authentication process as seen here.
Once "ANYdomain.com" is authenticated and valid in SendGrid, you can send mail from any_email@ANYdomain.com.
To send from "@ANYsubdomain.ANYdomain.com" you would need to follow the same domain authentication process linked above, but instead of using the "ANYdomain", you would use the full "ANYsubdomain.ANYdomain".
This will create records like "em####.ANYsubdomain.ANYdomain.com", which will need to be added to the DNS registrar for the root domain. This is the registrar for "ANYdomain.com" in this example.
Once the subdomain records are added and the subdomain is valid in SendGrid, you will be able to send from any_email@ANYsubdomain.ANYdomain.com.
With both the subdomain and domain authenticated, you would be able to send from both domains as needed. If you wish to send from a different subdomain, you will need to authenticate that one and the same way.