Message transfer over SMTP routing is performed as a point-to-point exchange between two servers. The sending SMTP server contacts the receiving SMTP server directly and establishes a two-way transmission channel with it. To send a message over SMTP:

1. The sending server checks the recipient's address, which is in the format localpart@domain, and looks up the domain in the Domain Name System (DNS).

2. DNS returns the Mail Exchanger (MX) record for the domain, indicating the IP address of the servers in the domain that accept mail over SMTP.

3. The sending server connects to the destination server over TCP/IP, establishes an SMTP connection on port 25, transfers the message, and closes the connection.

Enabling SMTP on the Domino server

Domino supports sending and receiving mail over SMTP by means of the SMTP listener task and SMTP Router, respectively, each of which you enable separately. The SMTP listener task handles incoming SMTP connections and delivers messages received over those connections to MAIL.BOX. It does not handle subsequent delivery or transfer of those messages. You configure the SMTP listener task for receiving mail on the Basics tab of the Server document. For more information about configuring Domino to receive SMTP mail from other servers in your organization and/or from the Internet over SMTP, see the chapter, "Setting Up Mail Routing."

The Router task for SMTP is the same Router task that handles Notes routing. When a message in MAIL.BOX requires transfer to another server, the Router determines where to send it and whether to send it over Notes routing or SMTP.

By default, SMTP is disabled. To configure Domino to use SMTP to send mail, you must change settings on the Router/SMTP-Basics tab of the Configuration Settings document. You can configure Domino to use SMTP when sending mail to destinations:

• Outside the local Internet domain
• Within the local Internet domain

On servers that support both SMTP and Notes routing, each time the Router detects a new message in MAIL.BOX, it chooses the protocol by which to transfer the message. The routing decision is based on the message's address and format, and whether the server is configured to send SMTP within the local Domino domain, outside the local Internet domain, or both.

Using SMTP to send mail to local domain addresses

Enabling SMTP within the local Domino domain allows the Router to consider SMTP as an alternative routing protocol when transferring mail to another Domino server in the same Domino domain. When configuring servers to send SMTP within the local Domino domain, you have the following options:

• SMTP allowed for MIME messages only - If the destination is a Domino server running the SMTP listener and the message deposited in MAIL.BOX is already in MIME format, the Router sends it using SMTP. Messages in Notes rich text format are sent over Notes routing.
• SMTP allowed for all messages - If the destination is a Domino server running the SMTP listener, the Router always uses SMTP when transferring a message to another Domino SMTP host, regardless of the message's current format. If a message deposited in MAIL.BOX is in Notes format, the Router converts the messages to MIME before sending.

By default, enabling SMTP within the local Domino domain allows the Router to use SMTP to transfer mail to any other Domino SMTP host in the same Domino domain. You can restrict the use of SMTP within the local domain so that SMTP is allowed only for message transfers that take place between servers in the same Notes named network. To set this restriction, use the field "Servers within the local Domino domain are reachable via SMTP over TCPIP" on the Router/SMTP - Basics tab of the Configuration Settings document.

If the receiving server is running the SMTP listener, servers configured to send SMTP within the local Domino domain always use SMTP to send MIME messages to destinations within the same Notes named network. For messages in Notes format, the Router sends SMTP only if the server is configured to send all messages over SMTP.

Sending SMTP outside the local Internet domain

Enabling Domino to send SMTP to external Internet domains allows the server to transfer outbound Internet mail either directly to a host in the receiving domain or indirectly to an Internet host.

If a message in MAIL.BOX has a recipient address that contains an @ sign and a domain part (the part of the address to the right of the @ sign) that does not resolve to the local Domino domain, the Router identifies the message destination as non-local. A non-local address can be an RFC 821 Internet address (where the domain part contains a period and is in the form localpart@org.domain) or an address in another Domino domain (including Foreign domains such as a pager or fax gateway).

To determine whether an Internet address is local, the Router checks whether the domain part of the address matches any of the local Internet domains defined in the Global Domain document in the Domino Directory. Local Internet domains include any domains listed in the Local primary Internet domain and Alternate Internet domain aliases fields in the Global Domain document. If there is no Global Domain document, the Router compares the domain in the recipient's address to the server's host name. For example, if the message is addressed to jdoe@mailhost3.acme.com and the Router is on the server mailhub.acme.com, the Router knows that the recipient is in the local Internet domain.

Connecting the Domino mail system to the Internet

Because Domino routes mail using the Internet-standard SMTP routing protocol, it's easy to configure the Domino system to send and receive mail from external Internet domains. For outgoing mail you can use a gateway routing architecture in which only designated servers use SMTP to route mail to external domains, or you can enable all mail servers to use SMTP to route mail to external domains. For inbound mail, you need to decide how to route mail coming in to your Internet domain from a firewall to Domino servers. How you set up inbound mail depends on whether your organization uses a single Internet domain name or multiple names and on the distribution of your servers.

For information on connecting Domino to the Internet, see the topics Preparing to send and receive mail to the Internet and Routing mail to external Internet domains.

Using a relay host

A relay host is an SMTP server or firewall that connects to the Internet and forwards, or relays, inbound or outbound Internet mail. A relay host can also be a DNS name that maps to multiple MX records. To configure Domino to use a relay host, you use two fields on the Configuration Settings document of the sending server. Add the relay's DNS or host name to the "Relay host for messages leaving the local Internet domain" field and enable "SMTP used when sending messages outside of the local Internet domain."

Using Notes routing to transfer outbound Internet mail to an SMTP server

On internal Domino servers that do not use SMTP to route mail, Domino uses Notes routing to transfer outbound Internet messages to a Domino SMTP server, which then transfers the messages to the Internet, either directly or through a relay host. To configure servers that use Notes routing to transfer Internet mail to a Domino SMTP server requires use of a Foreign SMTP Domain document and an SMTP Connection document.

See also

Configuring Domino to send and receive mail over SMTP
Setting up SMTP routing to external Internet domains
Setting up SMTP routing within the local Internet domain
Enabling a server to receive mail sent over SMTP routing
Configuring Domino to send mail to a relay host or firewall

Glossary