Most registrar (i.e., company that sell domain names) offer at least one email account with the domain name, it's the case for example with OVH or Infomaniak. Otherwise you could use a mail account from Proton or FastMail for example, they let you use your own domain name :).

Protonmail or apple mail allow you to use your own domain.

Or you could host your mailserver but that's never a good time.