Unoverica Message Transport v2.11 Chapter 5: Configuring Mail Routing

Chapter 5: Configuring Mail Routing

5.3.2 Configuring the External Site to Send Waiting Mail

Just as DNS servers publish IP addresses for hosts, they can also publish mail routing rules for hosts and domains as well. This is achieved through the use of Mail Exchange ("MX") resource records.

If you have your own domain name, but use an Internet Service Provider or other external site for mail queuing, then you will need to publish MX records for your domain. The MX records you use will depend on the connection to your Internet Service Provider or relay site. There are two common methods for implementing mail forwarding in relay environments:

MX records are created for your domain, indicating that the local mail server and the relay server are both able to receive mail for your domain. However, your mail server has a higher MX preference than the relay server. By setting a higher preference for your server, external sites will attempt to deliver mail to your system first, and then attempt delivery to the relay mail server after unsuccessfully connecting to you. The relay site will then collect the mail, but will see from the MX records that they are not the destination system. They will then hold the mail for you until a connection is established and they are able to complete the delivery process.
Some Internet Service Providers do not use MX records to control mail forwarding, but instead use rules and scripts to rewrite mail headers. They may be publishing their mail servers as the primary MX server for your site, and then rewriting the mail headers locally so that they are sent to your site after a connection is made.

You will need to discuss this with your Internet Service Provider or relay hosts to determine how they wish to advertise your site using MX records.

Since a wide variety of DNS servers run on an equally wide variety of platforms, it is impossible to describe how to add the records to the DNS server with any measure of accuracy. You should contact the system administrator, consultant, or service provider responsible for managing the DNS servers for your network and request that they add explicit MX records for this host to the DNS server, and to also add MX records for your domain to the DNS server as well. You will need to provide them with the IP address, hostname and domain name of this server.

For more information on DNS, refer to section C.3 The Domain Name System. For more information on MX records, refer to section C.3.2.2 "MX" Records.

NOTE: Depending on your connection to the relay site, you may or may not receive mail sent to your organization immediately. If you have a full-time or on-demand routed connection to the relay site, then mail should be delivered to your system immediately. However, if you do not have a full-time connection then you may have to use an alternative mechanism for having the mail sent to your network.

There are a couple of common mechanisms used for triggering mail delivery. Some Internet Service Providers add commands to their server-based login scripts that trigger an SMTP transfer. When you (or your router) logs into the Internet Service Provider network, these commands then initiate an SMTP transfer.

Another common option is to purchase a bi-directional, on demand connection. Some Internet Service Providers provide bi-directional on-demand routing at little extra cost. This allows their mail server to contact your mail server whenever incoming mail is received for your domain.

You will need to discuss these options with your Internet Service Provider to determine how they wish to initiate mail transfer sessions with your site. There are no configuration requirements with Unoverica Message Transport in order for you to use either of these mechanisms.

STEP: To continue to the next step in the configuration process, go to section 5.3.3 Adding the Domain to Unoverica Message Transport.