Setting up a smart host

A smart host is a directory server to which SMTP-routed messages are sent when the message recipient cannot be found in the Domino® Directory or other secondary directories configured on the server.

About this task

Typically, a smart host is used in organizations that employ multiple mail systems within a single Internet domain. Users on these systems may not be in the Domino Directory. For example, if some users are on a UNIX™ sendmail system but their inbound messages are routed through the Domino mail system, you can set up a smart host to ensure proper address resolution.

After you set up a smart host, when Domino receives a message, if the domain part of the recipient's address matches the local Internet domain or one of the alternate Internet domain aliases defined in the Global Domain document, the Router looks up the address against all configured directories. If the address is not found, the Router then uses SMTP to forward the message to the configured smart host.

Domino sends all messages addressed to unknown recipients in the local Internet domain to the configured smart host. You cannot configure Domino to send to the smart host only messages addressed to recipients in some subset of the internal domains and domain aliases defined in the Global domain document. Domino does not send messages addressed to unknown Notes® addresses to the smart host.

You must have DNS set up correctly to use a smart host.


  1. Make sure you already have a Configuration Settings document for the server(s) to be configured.
  2. From the Domino Administrator, click the Configuration tab and then expand the Messaging section.
  3. Choose Configurations.
  4. Select the Configuration Settings document and then click Edit Configuration.
  5. Click the Router/SMTP > Basics tab.
  6. Complete these fields, and then save the document:
    Table 1. Fields used to set up smart host



    Local Internet domain smart host

    The host name for the server that hosts the directory for SMTP recipients who are not in the local Domino Directory. To provide a level of failover and load-balancing, specify a host name that maps to an existing MX record. You can also specify IP address.

    Note: If this field contains a host name entry and the field Verify that local domain recipients exist in the Domino Directory is enabled, messages addressed to local recipients that can not be resolved are not accepted; therefore, there is no transfer of messages to the smart host.

    Smart host is used for all local Internet domain recipients

    Choose one:

    • Enabled to route all incoming SMTP messages to the smart host for lookup before routing elsewhere.
    • Disabled (default) to route only messages whose recipients are not found in the Domino Directory to the smart host for lookup.
    Note: If this field is set to Enabled, and the field Verify that local domain recipients exist in the Domino Directory is enabled, messages are received only for recipients whose names can be resolved in the Domino Directory. If this field is set to Enabled, and messages are accepted, all of these messages for local recipients are forwarded to the smart host.


The change takes effect after the next Router configuration update. To put the new setting into effect immediately, reload the routing configuration.