You can block and approve Domain/IP's or Email Addresses for Hosted Exchange within the Control Panel.
As a rule, you should not whitelist your own domain or addresses as this will leave you open to spoofing attacks and receiving spam from impersonators.
Add a Approved or Blocked Sender
- Log in to the Control Panel with your reseller account (https://controlpanel.hostedservices.com) and then log in as the relevant customer.
- Select More Services.
- Select MessageLabs.
- To always accept emails from a domain click Approved Senders. To always block messages from a domain click Blocked Senders.
- Click Add New Entry.
- Either enter either the domain, email address or IP address of the sender, and a short description.
- Click Submit.