If your domain registrar supports forwarding emails, I think you can continue to receive emails through a custom domain. Sending email with your custom domain

If your domain registrar supports forwarding emails, I think you can continue to receive emails through a custom domain. Sending email with your custom domain in the from/reply-to address is a different business, I recall it requires getting gmail to verify that you can receive via that custom address, and also set the mail server to smtp.gmail.com port 587.