Hello, I am going to be building out a website for a customer who has an email address that is @his website address. How do I transfer this over in duda?
Email does not transfer. It is separate from the website service. Assuming you only update the necessary A records and CNAME records on the client's domain, their email should remain unchanged.
Tom is correct here, the domain is managed outside of Duda, and in order to connect their Duda site to the domain, they only have to change the DNS records of the site. They don't need to touch the email records, so they can continue managing their email domain through their domain management platform.