TCP/IP Configuration and Management Manual

NonStop TCP/IP Processes and Protocols
TCP/IP Configuration and Management Manual—427132-004
B-29
Simple Mail Transfer Protocol (SMTP)
SMTPSND
A separate process (called SMTPSND) is started by the system administrator as part
of the NonStop TCP/IP startup mechanism. The SMTPSND process starts a session
with TRANSFER by logging in as SMTPGATE (the gateway correspondent). The
SMTPSND process then scans its INBOX for queued-up mail messages. Each
message is examined for identifying recipients. If the recipient is SMTPGATE, the real
recipient is the user specified in the suffix.
A connection is opened to the host specified for the recipient, and the message is sent
to that host. If the host cannot be reached at that time, the message is filed in the
RETRYFOLDER. One entry is made in the retry folder for each recipient to whom the
mail could not be delivered directly from the INBOX. This mechanism limits retry
messages to only those users who have still not received the message.
If the host is unknown, the message is returned to the sender specified by TRANSFER
with the notation “ERRORDELIVERING SMTP MAIL” in the subject line. The original
message is added as an attachment.
If the INBOX is empty, the RETRYFOLDER is scanned. If the RETRYFOLDER is
empty, the SMTPSND waits for 5 minutes (default) or the time specified in the
-time
parameter when the SMTPSND was started.
If the SMTPSND process runs out of memory, it restarts itself using the name specified
in the RUN command (if one is specified). This mechanism allows the SMTPSND
process to recover from memory failures without affecting the delivery of any
messages.
After changing the configuration file (SMPTCONF), you must restart the SMTP server.
Restarting the SMTP server or client does not cause any loss of messages.
The basic intelligence in the SMPTSND and SMTPRCV is the address parsing
mechanism. This mechanism is driven from the configuration file
$SYSTEM.ZTCPIP.SMTPCONF. This file can parse all legal FC 822 addresses. The
system administrator can modify the configuration file to change addresses.
For a detailed description of the operation of the SMTP server and client, refer to the
TCP/IP Applications and Utilities User Guide. For more detailed technical information
on the SMTP, refer to RFC 821 (
DDN Protocol Handbook, Volume 2, DDN Network
Information Center, December, 1985, pp 2-809 through 2-880). Also, refer to the book
Internetworking with TCP/IP (Douglas E.Comer, Prentice Hall, 1991).