By default, Microsoft SMTP Service blocks computers from relaying unwanted mail to a remote domain. To enable relay access to the domain, select the option in the Domain Properties property sheet.
The relay setting for a domain can override the site relay access settings. You can block relay access for the site yet allow it for one domain, or vice-versa. For more information about site relay access, see Removing Relay Restrictions from a Site.
Note This feature is not available in Internet Service Manager (HTML).
To allow relay access for a remote domain