Specifying how Domino® looks up SMTP hosts when sending outbound mail

You can specify how the Router determines the IP address(es) for destination SMTP systems (for example, the Internet). Known as address resolution, the method you select determines how the Router performs domain-name-to-IP-address translation.

About this task

Address resolution methods are:

  • Dynamic lookup only (DNS only)
  • Local lookup only
  • Dynamic then local

If you configure TCP/IP to use the Domain Name System (DNS), select Dynamic mapping only or Dynamic then local. For Dynamic mapping only, the Router queries a DNS server to map a fully qualified host name to an IP address.

For Dynamic then local, the Router first queries the DNS and then checks a file on your local drive. This file, known as a hosts file, maps destination host names to IP addresses. The Dynamic then local option can be useful if you need to connect to internal hosts that are not listed in the DNS.

If you configure TCP/IP to use local hosts lookup, select Local lookup only. If you use this option, the IP address and fully qualified host name for each destination must exist in the hosts file. This option requires more administrative attention than the Dynamic mapping only option because you need to maintain the file.

If the DNS does not list a destination host name, the Router designates the message as non-deliverable. If the DNS is unavailable, the Router retries delivery up to the configured number of times as indicated in the Initial transfer retry field on the Configuration Settings document.


  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 to be edited and then click Edit Configuration.
  5. Click the Router/SMTP tab.
  6. On the Basics tab, choose on of the following for the Host name lookup field, and then save the document:
    • Dynamic lookup only (DNS only) - The Router determines the IP address for a host by looking it up in DNS. SMTP transfer can occur only if the destination host is listed in DNS.
    • Local lookup only (host files only) - The Router determines the IP address for a host by looking it up in a hosts file on the local machine.
    • Dynamic then local - (default) The Router determines the IP address for a host by looking it up in DNS first and then checking the local hosts file if no DNS entry exists.


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