# Custom domains

By default, participants open the signing flow at `sign.docue.com` and receive invitation emails from Docue's sender address. You can use your own domains instead:

- **UI domain** — serves the hosted Sign UI from your hostname, such as `sign.acme.com`.
- **Email domain** — sends invitation and notification emails from your address, such as `sign@mail.acme.com`.


## Register your domains

Custom domains are registered for your workspace by Docue. Contact [support@docue.com](mailto:support@docue.com) with:

- The hostnames you want to use, and whether each one is for the UI or for email.
- Whether you need them in sandbox, production, or both. Domains are registered separately for each environment.


Docue will guide you through the DNS and mail sending setup each domain needs.

## Use a domain in a signing session

Set `ui_domain` and `email_from` when you [create a signing session](/embed-api/openapi/signing/createsigningsession). Both fields are optional and independent of each other.

```json
{
  "document_name": "Employment Agreement",
  "ui_domain": "sign.acme.com",
  "email_from": "\"Acme\" <sign@mail.acme.com>",
  "participants": [...]
}
```

- `ui_domain` must exactly match a UI domain registered for your workspace. Signing URLs for the session, including those in emails, SMS messages, and manual invitations, use this hostname.
- `email_from` can be a plain address, such as `sign@mail.acme.com`, or include a display name, such as `"Acme" <sign@mail.acme.com>`. The domain part of the address must be an email domain registered for your workspace.


If a domain is not registered for your workspace in the environment of your API key, the request fails with `422 Unprocessable Content`.

The domains are set per session and cannot be changed after the session is created. Session responses return them in `ui_domain` and `email_from`, or `null` when the defaults are used.

If a domain is later removed from your workspace, sessions that used it fall back to the default Docue domain and sender.