TCP/IP Configuration and Management Manual

NonStop TCP/IP Processes and Protocols
TCP/IP Configuration and Management Manual—427132-004
B-28
Simple Mail Transfer Protocol (SMTP)
The SMTP gateway also can relay SMTP messages between SMTP hosts. Acting as
an intermediate node, it can store and forward SMTP messages. Messages received
by the gateway from one SMTP host to be relayed to another SMTP host are first sent
to TRANSFER.
TRANSFER treats the SMTP gateway as a mail correspondent (SMTPGATE).
Messages from TRANSFER hosts to SMTP hosts, or from one SMTP host to another
SMTP host, are sent to the gateway’s mail correspondent ID on the gateway node. the
address suffix contains the SMTP host destination path. TRANSFER messages are
addressed as follows:
corresponden_name [@node] [(suffix)]
The SMTP processes SMTPRCV and SMTPSND (described below) first open the
T1SERV (Transfer Process) $ZCC0. They then start a session with TRANSFER by
logging in as the SMTP MAIL gateway correspondent. Once the processes log into
TRANSFER, they can make requests to TRANSFER to store, retrieve, or delete
messages. The mail correspondent name and password are specified in the
SMTPCONF configuration file, as described in Configuration Files in the Guardian
Environment on page 3-34.
The process that handles mail arriving from the network (Internet) is started by the
LISTNER process, which listens for incoming service requests on well-known ports.
the well-known port number for SMTP services is TCP port 25. This port number is set
up in the PORTCONF configuration file for the LISTNER process by adding a entry for
SMTP, as described in Configuration Files in the Guardian Environment
on page 3-34.
SMTPRCV
When a connection request is received, LISTNER starts another process (called
SMTPRCV), which handles requests for a single SMTP connection. The SMTPRCV
process creates a new socket and accepts the connection.
The SMTPRCV process establishes a session with TRANSFER, logging in as the
gateway mail correspondent. When logging into TRANSFER, SMTPRCV specifies the
suffix as the sender of the mail message. This mechanism enables a local recipient to
reply to a message when it is received.
The SMTPRCV process verifies the recipient specified through TRANSFER. If the
recipient is on another SMTP host, SMTPRCV specifies the gateway correspondent
(with a suffix) as the recipient of the message.
SMTPRCV collects the RFC 822 header into a separate attachment. This attachment
appears at the end of the message. The subject line appears as a TRANSFER subject
line, followed by the body of the message. The header is submitted to TRANSFER at
the end of the data.
Note. Because the password is specified in the configuration file, be sure to secure it so users
cannot access the SMTP mail correspondent password.