All Boundless apps are able to send emails by default from a shared app domain. As your company grows or depending on your workflow it is often desirable to send email from your own domain.
You can connect Boundless to send emails from your own domain under Settings -> Email.
Using a service like SendGrid or Mailgun you can get these SMTP credentials which will allow you to send emails from your own domain.
With Mailgun you can find and manage these credentials under Sending -> Domain Settings -> SMTP Credentials.