Interface to a User Mail System
This section describes the interfaces between the Cisco IOS for S/390 mail
routines and the post office in more detail.
Receiving Mail
The post office receives a message from the network by retrieving it from a
JES SYSOUT file where it was previously spooled by SSMTP (described in the
following section). The post office can retrieve these JES SYSOUT files using
one of the following:
- The MVS-provided or a user-written external writer
- The JES Sub-System Interface (SSI)
SSMTP
SSMTP begins execution when it receives a request to connect to the
well-known mail port. SSMTP completes the opening of the TCP connection and
performs the receiver end of the SMTP protocol. When a message is received,
SSMTP spools it into a JES SYSOUT file from which the post office retrieves it.
A secondary copy of the message text is also spooled into a SYSOUT file destined
for the local printer. Normally, this copy is deleted at deallocation time.
However, if the received message exceeds a configuration-specified size, the
primary copy (destined for the post office) is deleted and the secondary copy
queued for printing. This is called diversion of the mail to the printer. (In
the case where no post office is implemented, all received mail is diverted to
the printer.) Both of the JES SYSOUT files have RECFM=VB (in other words, no
carriage control).
SSMTP prepends an envelope to the messages it spools to JES.
The envelope consists of a single X-from: field of the form:
X-from: remote user@remote host
followed by one or more X-to: fields of the form:
X-to: TSO userid@local post office name
The X-from: field contents are taken directly from
the SMTP MAIL FROM: command. The X-to: field contents are derived from a single
RCPT TO: SMTP command. The local part of the mail address from the RCPT TO:
command is mapped into a TSO user ID using the SMTP User Table. If the local
part of the mail address is not in the SMTP User Table, SSMTP rejects the
recipient mail address. The local post office name is an SSMTP configuration
parameter that represents the name of the local post office. It need not be the
same as the local network host name.
Usage Guidelines
The MAIL FROM: command received by SSMTP generates the X-FROM: line. The RCPT
TO: commands received by SSMTP generate the X-TO: lines. The rest of the text of
the file is placed into the file as received after the DATA command.
ASCII format effectors in the input stream are generally handled as follows:
- Horizontal tabs (HT) are expanded to blanks assuming tab stops in
every 8th column: 8, 16, 24, 32, etc.
Other format effectors (FF, a LF not following a CR, a CR not preceding a
LF>, a BS) appear in the spooled file as the corresponding EBCDIC control
characters.
SSMTP supports the following SMTP commands: HELP O, MAIL, RCPT, DATA, VRFY,
QUIT, RSET, NOOP, HELP. This is the minimum implementation set.
SSMTP does not support expanding mailing lists.
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