A forwarder is a name plus a destination, and both halves have to be real
An address on your own domain is the cheapest thing you can do that makes you look like you have been working longer than you have. you@yourname.com on a submission reads differently from a numbered free account, and casting people notice without being able to say why.
What is happening behind it
Most custom addresses for actors are forwarders rather than mailboxes. A forwarder has two halves. There is the name on your domain, which is what people type. And there is the destination, which is a real inbox you already read every day. Mail arrives at the first and is delivered to the second. You never log in anywhere new, which is the entire appeal.
Both halves have to be real for anything to arrive. That sounds obvious and it is the failure mode: a system that creates the name and never records a destination produces an address that exists, accepts nothing, and reports itself as working. The destination now comes from your account, using your listed contact address and falling back to the email on your account itself. An address that would forward to itself is refused, because that is a loop rather than a delivery.
Which domains you can create on
You can create an address on your own domain, and on the shared forwarder domains you have opted into. Not on anybody else's. That check is the boring kind of correctness that nobody sees working: the domain you ask for is verified against the domains that are actually yours before anything is created.
There is one implementation of "make an address" behind both the settings page and the standalone tool, so an address created from either place is the same address, appears in the same list, and is managed the same way.
Setting one up
If you have a domain connected already, the address is a few fields. If you do not, connecting a domain is the step before this one, and choosing the domain is the step before that. Actors who want more than one address should read the note on multiple domains.
Two related pieces are worth your time once the address exists. Why a clean email address matters covers what to name it, which people get wrong more often than they get the technical side wrong. And the signature builder puts something professional underneath every message you send from it. If email is the part of your setup you have been avoiding, this is the case for fixing it.
