Sender domain is the address which recipients see in the ‘from’ field when they open your emails. For example: when you receive the activation mail of Pepipost, the from address is ‘email@example.com’ wherein “pepipost.com” is the sender domain.
To start sending emails to your customers, you can either use your top-level domain (e.g. mycompany.com) or a sub-domain like email.mycompany.com.
To start sending emails, you need to add and verify your sending domains. The verification is done to ensure your sending domain’s security.
Go to Settings --> Sending Domains
In Add your Domains field, type the name of the domain that you want to add. e.g. mydomain.com.