Overview of routing mail using SMTP

Enabling SMTP on the Domino® server

Domino® supports sending and receiving mail over SMTP by means of the SMTP Router and SMTP listener task, 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.

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

How the Router determines when to use SMTP

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.

When the Router picks up a message in MAIL.BOX, it reads the address to determine whether the recipient is in the local domain. If the recipient is local, the Router looks in the ($Users) view of the Domino® Directory for a Person document containing that address. If SMTP is allowed within the domain and the message format matches the format specified in this setting, the Router uses TCP/IP to connect to the destination server, establishes an SMTP connection, and transfers the message.

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 that follows 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.renovations.com and the Router is on the server mailhub.renovations.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.

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.