PLANNING
The Domain Name System (DNS) is a directory used by SMTP to convert a name, such as renovations.com, to a list of servers that can receive connections for that name and to find the IP address of a specific server. By looking up a destination server's address in the DNS, the sending server can properly route a message to a recipient.
DNS uses two kinds of records: Mail Exchanger (MX) records and A records. An MX record maps a domain name to the names of one or more mail hosts. An A record maps a host name to the IP address of a server.
Mail servers also use other DNS records. For example, servers that receive Internet mail perform a reverse lookup to a DNS PTR record to determine the host name for a given IP address. Reverse lookups are useful in verifying the source of a message, an important tool for restricting relay access through your server or preventing unsolicited commercial e-mail (UCE).
You must correctly configure DNS to support your use of SMTP. To determine the IP address of the mail server for the destination domain, HCL Domino® does the following:
1. The server looks up the domain part of each recipient's address in DNS.
2. If DNS finds an MX record, the server tries to connect to the server listed in that MX record. If there is more than one MX record, the server tries to connect to the record that has the lowest cost. If more than one MX record has the lowest cost, the server randomly selects one and tries to connect to the server listed in that MX record.
4. If DNS does not find a record, Domino cannot deliver the message and sends a nondelivery message to the sender.
An MX record maps a domain name to one or more host names. An A record maps a host name to the IP address of a server. You may want to use a host name in the MX record instead of just an A record for the following reasons:
For example, the renovations.com domain has four MX records:
Parent topic: Messaging overview
Related concepts Restricting SMTP inbound routing
Related tasks Specifying how Domino looks up SMTP hosts when sending outbound mail Using a Global Domain document to set up a server to receive mail for multiple Internet domains Restricting inbound SMTP connections