Once a custom domain is active on your account, you can use it when creating aliases. The process is the same as creating any alias — the domain selector just has more options.
Selecting your domain
When you create a new alias at Aliases → New Alias, there's a domain dropdown next to the alias name field. It lists all your active custom domains alongside the default brand domains. Pick your domain from the list.
The alias address preview updates as you type, so you can see exactly what the full address will look like before you create it.
What it looks like
Instead of shop.a3f9k2@aliasfleet.me you'd get something like shop@yourdomain.com — or whatever alias name and domain you chose.
Changing the domain on an existing alias
You can't change the domain on an existing alias. The address is fixed at creation. If you need the same alias name on a different domain, you'd have to create a new alias and delete the old one.
If your domain disappears from the selector
The domain only appears if it's in Active status. If it's showing as DNS Pending or Setup Required, finish the DNS setup first. See Domain status and health.
Setting a default domain
In Settings you can set a default domain for new aliases. If you mostly use your custom domain, set it there so it's pre-selected every time instead of having to change the dropdown manually.