Configuring Domino® to send mail to a relay host or firewall

A relay host can be a server within your organization that routes messages addressed to destinations outside the local Internet domain. Often the same server acts as a firewall through which your organization funnels all messages outbound to the Internet. It can be an HCL Domino® server or another type of server -- for example, a UNIX sendmail server.

About this task

To configure internal SMTP servers to send mail to a relay host, you specify the IP address or host name of the relay host in the Configuration Settings document. If connections from the internal mail server to an ISP mail server pass through a firewall, specify the internal interface of the of the firewall in this field, and configure the firewall to forward traffic received on port 25 to the ISP mail server.

Servers that do not route mail over SMTP require special configuration to transfer messages to a relay host or firewall.

Configuring multiple relay hosts

About this task

To enable greater control over outbound message routing, you can configure multiple relay hosts. Using multiple relay hosts enables Domino® to route mail addressed to certain Internet domains to certain relay hosts, without first performing a DNS lookup. For example, you can split external SMTP mail routing so that Domino® routes all outbound Internet mail along one path, except mail addressed to a specific domain, such as *, which it sends through a specific SMTP server.

To configure multiple relay hosts, create a Foreign SMTP Domain document for each set of destinations, and then create SMTP connection documents to match these foreign SMTP domain documents. For example, using the previous example, you would create one Foreign SMTP Domain document for *.* and another for *

Foreign SMTP Domain documents are used by servers that route mail over SMTP as well as those using NRPC. For servers that use SMTP routing, Foreign SMTP Domain document indicate the destinations that need relay hosts and the relay hosts to use in each case.

To set up a relay host

Before you begin

Make sure you already have a Configuration Settings document for the server(s) to be configured.


  1. From the Domino® Administrator, click the Configuration tab and then expand the Messaging section.
  2. Choose Configurations.
  3. Select the Configuration Settings document and then click Edit Configuration.
  4. Click the Router/SMTP > Basics tab.
  5. For the field Relay host for messages leaving the local Internet domain enter the host name, domain name, or IP address of the server being used as a relay host keeping the following guidelines in mind:
    • You can specify a domain name to provide load-balancing between relay hosts. This approach to load balancing requires that the internal DNS contain an MX record for the domain that can resolve to a host name. If this isn't the case, see the following procedure for an alternative approach. When using the MX record approach, router logging is more legible.
    • When entering an IP address, do not enclose it in brackets or include spaces.
  6. Click Save & Close.
  7. Reload the routing configuration to put the new setting into effect immediately. Otherwise, the change takes effect after the next Router configuration update.

What to do next

After you set up a relay host, you can set up restrictions based on where the message originated or the message destination.

Load-balancing between relay hosts without a domain MX record

About this task

As described in the previous procedure, you can configure load balancing between relay hosts by specifying a domain name in the Relay host for messages leaving the local Internet domain field. This approach requires that the internal DNS contain an MX record for the domain that can resolve to a host name. If you can't meet this requirement, you can instead configure load balancing by specifying multiple host names or IP addresses in the field.

Use commas and semicolons as delimiters between hosts. To configure the router to connect to hosts in a random order, use commas. To group hosts in a preferred connection order, use commas and semicolons.

Assume this example:,;;,,

In this example, the router tries to connect to the hosts listed before the first semicolon (host1 or host2) in a random order. If neither host responds, the router tries to connect to hosts listed before the second semicolon, in this case a single host (host3). If that host doesn't respond, the router tries the final group of hosts (host4, host5, or host6) in a random order.