.TH smail "" "" Command
.PC "Mail delivery system"
\fBsmail [ \fIflags \fB] \fIaddress ...\fR
.PP
.B smail
is the program that receives and delivers mail.
It accepts mail from a source either on your local host or on a
remote host, and delivers that mail to its destination \(em again, either
on your local host or another remote host.
.B smail
does not provide a user interface for
typing mail or reading it;
to do so, you must use a ``mailer'' program, such as
.B mail
or
.BR elm .
.PP
You will rarely, if ever, need to invoke
.B smail
directly.
You may modify one of its configuration files from time to time, but
.B smail
normally is invoked only by other programs.
The rest of this article gives
.BR smail 's
command-line options and describes how it works.
You will find this information
useful should you wish to reconfigure your mail system, or chase down a bug.
.PP
.B smail
can be invoked under a variety of names.
Each name indicates the major use to which
.B smail
will be put, e.g., receiving local mail, receiving remote mail,
attempting to deliver undelivered mail, or displaying information about
undelivered mail.
These names are described below; each also has its own Lexicon entry.
.SH "Command-line Options"
.B smail
recognizes the following command-line options:
.IP \fB\-bc\fR
Display the contents of file
.BR COPYING ,
which is distributed with the source code for
.BR smail .
This file details what your rights and restrictions the authors of
.B smail
have set upon their work.
.IP \fB\-bd\fR
Listen for connection requests on a socket bound in the Internet domain.
.II SMTP^definition
.II "Simple Mail Transfer Protocol"
When a connection occurs, conduct an Simple Mail Transfer Protocol (SMTP)
conversation with the peer process on the other system.
This option currently is not implemented under \*(CO, as
\*(CO does not yet support networking.
.IP \fB\-bi\fR
Initialize the
.B aliases
file.
The file that it builds depends upon whether you also use option
.B \-oA
on the command line.
.IP
By default,
.B smail
under \*(CO
is compiled with the
.B GDBM
package.
.B GDBM
is a set of functions that permit a program to build and read a simple
hashed data base; for details on how it works, see the Lexicon entry for
.BR libgdbm .
Thus, when you also use option
.BI \-oA file
to name an aliases file,
.B smail
invokes the command
.B /usr/lib/mail/newaliases
to compile the contents of
.I file
into a DBM data base.
.IP "\fB\-bm \fIaddress ...\fR
Deliver mail to each
.IR address .
.IP "\fB\-bP \fIaddress\fR"
Assume that each
.I address
on the command line is a configuration-file variable,
and write its value onto the standard output.
For example, the command
.DM
	smail -bP hostnames max_message_size
.DE
.IP
produces output of the form:
.DM
	lepanto.com
	102400
.DE
.IP
If you also use the flags
.B \-d
or
.B \-v
on the command line,
.B smail
also displays the variable names.
Thus, the command
.DM
	smail -bP -v max_message_size
.DE
.IP
prints something like the following:
.DM
	max_message_size=102400
.DE
.IP
The command
.DM
	smail -bP primary_name
.DE
.IP
prints the primary (or ``canonical'') name for the local host that
.B smail
uses, and command
.DM
	smail -bP config_file
.DE
.IP
prints the name of the primary configuration file.
The command
.DM
	smail -bP help
.DE
.IP
prints a verbose listing of every variable plus its type,
one variable per line.
Finally, command
.DM
	smail -bP all
.DE
.IP
prints a verbose listing of every variable and its value.
It is equivalent to the command
.B "smail \-bP \-v"
followed by a list of the name of every configuration variable.
.IP \fB\-bp\fR
List information about the messages that currently reside in
.BR smail 's
input spool directories.
.II mailq
This is 
.BR smail 's
default mode of operation when you invoke it under the name
.BR mailq .
When you also use the flags
.B \-v
or
.BR \-d ,
.B smail
displays the transaction-log entries for each message,
to show what has happened to the message so far.
.\" HUH???
.\".IP \fB\-bR\fR
.\"Enter the mail domain of giant mail messages and RFC standard scrolls.
.\"Attempt to make it down to protocol level 26 and back.
.IP \fB\-bS\fR
Read SMTP commands from the standard input, but do not write SMTP
replies onto the standard output.
Report failures via mail rather than through reply codes.
.IP
This option is suitable for setting up a batched form of SMTP between
machines over a remote execution service like \*(UU.
.II rsmtp
This is the
default mode of operation if you invoke
.B smail
under the name
.BR rsmtp .
.IP \fB\-bs\fR
Read SMTP commands from standard input, and write SMTP replies onto
the standard output.
The following SMTP commands are implemented:
.DS
.ta 0.5i 1.5i 2.5i 3.5i
.B
	HELO	MAIL	FROM	RCPT
	TO	DATA	RSET	NOOP
	VRFY	EXPN	QUIT
.DE
.IP
.II smtpd
This is the default mode of operation if you invoke
.B smail
under the name
.BR smtpd .
.IP \fB\-bt\fR
Run
.B smail
in test-address mode:
.B smail
reads addresses from standard input, parses them,
and writes its result onto the standard output.
This is primarily useful for debugging
.B smail
or debugging new
.B smail
routers.
.IP \fB\-bV\fR
See option
.BR \-V ,
below.
.IP \fB\-bv\fR
Verify an address.
.B smail
reads each address you list on its command line, subjects it
to aliasing and forwarding expansions, then subjects it to host routing
or resolving,
and finally prints the resolved address onto the standard output.
You can then check whether the resolved address matches what you expect.
If
.B smail
cannot resolve an address, it prints an explanation of why it cannot.
.IP "\fB\-C \fIfile\fR"
Use
.I file
as the primary configuration file \(em i.e., the file that
holds global attributes.
.B smail
resets the effective user identifier and group identifier
to those of the real user and group, to avoid
problems should
.B smail
be
.B setuid
to the superuser.
.IP
If
.I file
is `-', then
.B smail
does not use a primary configuration file.
You should use this only for debugging.
.IP "\fB\-d[\fInumber\^\fB]\fR"
Turn on debugging.
.I number
sets the level of debugging; the default level is one.
No white space must separate the option and
.IR number .
Please note that
.B \-d
and
.B \-v
are identical;
.B smail
recognizes both for historical reasons.
.IP "\fB\-D \fIfile\fR"
Write debugging information into
.IR file .
Normally, using option
.B \-v
or
.B \-d
to generate debugging output also disables background delivery of
mail, because programs should not continue to write to the standard
error after the mail process exits; however, if you name a
debugging-output file, background delivery can continue.
.IP \fB\-ee\fR
.IS \fB\-oee\fR
.II berkenet
These options refer to a ``berkenet'' style of error-processing that
.B smail
does not support.
If used,
.B smail
mails an error message back to you.
.IP \fB-em\fR
.IS \fB\-oem\fR
Mail error messages to the sender.
This is the default.
.IP \fB\-ep\fR
Write error messages onto the standard-error device.
.IP \fB\-eq\fR
If an error occurs, do not notify the sender of it.
This only works for mail being delivered locally:
an error that occurs on a remote host's mail system still
generates a mail message to the sender.
To set this behavior on both the local host
and a remote host, supply a header that reads:
.DM
	Precedence: junk
.DE
.IP \fB\-ew\fR
.IS \fB\-oew\fR
Mail errors to the sender, just as with option
.BR \-m .
With some mail-delivery programs,
this option asks the program to invoke the command
.B write
to write errors onto the sender's screen, should she be logged in.
.IP "\-F \fIfullname\fR"
Set to fullname the full name of the sender for incoming mail.
Use this option only if you wish to use smail to receive a single mail
message from the standard input.
.IP "\fB\-f \fIsender\fR"
Set to
.I sender
the address for incoming mail.
Use this option only if you want
.B smail
to receive a single mail message from the standard input.
.IP "\fB\-h \fInumber\fR"
Set to
.I number
the hop count for a message.
If this command-line option is not used,
.B smail
computes the hop count from the number of
.B Received:
fields in the message's header.
.B smail
uses the hop count as a primitive method of detecting an infinite loop:
if the hop count is too large,
.B smail
rejects the mail.
.IP
NB, an infinite loop occurs when two sites each think that a given
user resides on the other.
A message mailed to that user will ping-pong
between the sites; unless the message is stopped somehow, its
header can grow infinitely large.
.IP \fB\-I\fR
Use the ``hidden-dot'' algorithm when reading a message.
If a message contains a line that begins with one or more periods,
.B smail
removes that leading period; a line that consists of a single period
terminates the message.
This option is always set for messages received via SMTP.
.IP \fB\-i\fR
A line that consists of a single period does not terminate an incoming
message.
.II rmail
This is the default if you invoke smail under the name
.BR rmail .
.IP \fB\-m\fR
If a user mails a message to an alias list or mailing list that
includes her name, send a copy of the message to that user.
By default,
if the user mails a message to a list that includes her name,
.B smail
does
.I not
send a copy of a message back to her.
.IP \fB\-N\fR
Disable delivery of a message.
.B smail
performs all other processing,
and the transport programs are expected to go through most of the
steps involved in delivery.
Use this option when you wish to debug
smail but do not want to have the messages delivered.
.IP \fB\-n\fR
Do not process aliases.
With this option,
.B smail
will not expand entries in alias files;
however, it will still expand entries in mailing-list files and forwarding
files.
.IP "\fB\-oC \fIfile\fR"
See option
.BR \-C ,
above.
.IP \fB\-odb\fR
If mail is to be delivered, deliver it in the background.
Note that background delivery is not currently supported in the SMTP modes:
mail is delivered in the foreground.
.IP "\fB-oD \fIfile\fR"
Use
.I file
as the
.B directors
file, instead of the default
.BR /usr/lib/mail/directors .
.B smail
resets the effective user and group identifiers to those of the real user
and group, to avoid problems
should an installation setuid
.B smail
to the superuser.
If file is `-',
.B smail
does not read a
.B directors
file.
Use this option only when
you are debugging
.BR smail .
.IP \fB\-odf\fR
If mail is to be delivered, deliver it in the foreground.
.IP "\fB-oE \fIfile\fR"
Use
.I file
as the delivery-retry control file, instead of the default
.BR /usr/lib/mail/retry .
.B smail
resets the effective user and group
identifiers to those of the real user and group, to avoid problems
should an installation setuid
.B smail
to the superuser.
If file is `-',
.B smail
does not read a retry file.
Use this option only when you
are debugging
.BR smail .
.IP \fB\-oep\fR
See option
.BR \-ep ,
above.
.IP \fB\-oeq\fR
See option
.BR \-eq ,
above.
.IP \fB\-oI\fR
See option
.BR \-I ,
above.
.IP \fB\-oi\fR
See option
.BR \-i ,
above.
.IP "\fB-oL \fIdirectory\fR"
Use
.I directory
as the library directory \(em that is, the directory
that holds configuration files and mailing-list directories.
This overrides the default value compiled into
smail through its option
.B smail_lib_dir
(under \*(CO
.BR /usr/lib/smail ),
as well as any name set in a configuration file.
.IP "\fB\-oMr \fIsender_proto\fR"
Use
.I sender_proto
as the protocol by which sending host delivers the mail message.
You can include this value in expansion strings via the variable
.BR $sender_proto .
.IP "\fB\-oMs \fIsender_host\fR"
Set to sender_host the system that can send the mail message.
You can include this value in expansion strings via the variable
\fB$\fIsender_host\fR.
.IS \fB\-om\fR
See option
.BR \-m ,
above.
.IP "\fB\-oQ \fIfile\fR"
Set the path name of the host-name qualification file to
.IR file ,
instead of the default
.BR /usr/lib/mail/qualify .
.B smail
resets the effective user and group identifiers to those of the
real user and group, to avoid problems should an installation setuid
.B smail
to the superuser.
If
.I file
is `-',
.B smail
does not read a qualify file.
Use this option only when you are debugging
.BR smail .
.IP "\fB\-oR \fIfile\fR"
.II /usr/lib/mail/routers
.II routers
Use
.I file
as the router file, instead of the default
.BR /usr/lib/mail/routers .
.B smail
resets the effective user and group identifiers to the real user
and group identifiers, to avoid problems should an installation setuid
.B smail
to the superuser.
If file
is `-',
.B smail
does not read a router file.
Use this option only when you are debugging
.BR smail .
.IP "\fB\-oT \fIfile\fR"
.II /usr/lib/mail/transports
.II transports
Use
.I file
as the transport file, instead of the default
.BR /usr/lib/mail/transports .
.B smail
resets the effective user and group identifiers to those of the
real user and group, to avoid problems should an installation setuid
.B smail
to the superuser.
If file is `-',
.B smail
does not read a transport file.
Use this option only when you are debugging
.BR smail .
.IP "\fB\-oU\fR"
Tell
.B smail
to report memory usage when it exits.
.IP "\fB\-oX \fImail-service\fR"
.II TCP/IP
Tell
.B smail
to listen for SMTP requests on the TCP/IP service or port
.IR mail-service .
You can use this option with
.B \-bd
mode to define alternate debugging versions of 
.BR smail 's
SMTP listening daemon; this can be useful when you test a new installation.
.IP
Please note that because \*(CO does not yet support networking, this
option does nothing.
.IP \fB\-Q\fR
.IS \fB\-odq\fR
Spool incoming messages, but do not deliver them until later queue.
This mode of operation is somewhat more efficient in terms of CPU
usage, but slows down the flow of mail.
.IP "\fB\-q[\fIinterval\^\fB]\fR"
Force
.B smail
to process its input spool directory.
If you set
.IR interval ,
.B smail
continually checks its input\-spool directory,
and sleeps for
.I interval
between checks.
.I interval
is a string that consists of a number
followed by one of the following letters to indicate unit of time:
.DS
	\fBs\fR	seconds
	\fBm\fR	minutes
	\fBh\fR	hours
	\fBd\fR	days
	\fBw\fR	weeks
	\fBy\fR	years
.DE
.IP
For example, option
.B \-q2h30m
tells
.B smail
to check its input spool directory every two hours and 30 minutes.
This flag is useful with the
.B \-bd
mode of operation, as it awakens the daemon process after each
interval to process the queue.
.II runq
This is 
.BR smail 's
default mode of operation when you invoke it under the name
.BR runq .
.IP "\fB\-r \fIsender\fR"
See option
.BR \-f ,
above.
.IP \fB\-t\fR
Extract addresses from the
.BR To: ,
.BR Cc: ,
and
.B Bcc:
fields of the message header.
This is useful for mailers that do not compute the recipient addresses
themselves.
In this mode, the addresses given on the command line
will not receive mail, even as a result of expanding
aliases or forwarding addresses.
.B smail
ignores this option unless it is in the mode
set by command-line option
.B \-bm
(which is the default mode).
.IP \fB\-V\fR
Print the version smail onto the standard output.
.SH "Normal Use"
A user agent can submit new mail message by invoking
.B smail
and passing it a message via the standard input.
For example, mailers such as
.B mail
and
.B elm
submit mail by invoking
.B smail
with a command such as
.DM
	smail -em -i \fIaddress\fP ...
.DE
.PP
Because
.B smail
also works correctly if invoked as
.BR sendmail ,
it is common to install
.B smail
as
.BR /usr/lib/sendmail ,
so that existing binaries on BSD systems, or other systems that currently run
.BR sendmail ,
need not be modified to run
.B smail
instead.
.II sendmail
This also lets you run applications that have been configured to send mail via
.B sendmail
without modifying their sources or recompiling.
.PP
Some user agents, such as GNU Emacs, may wish to have
.B smail
decipher the recipient list from the header.
These programs can invoke
.B smail
with a command, such as:
.DM
	smail -em -t -i
.DE
.PP
.II uuxqt
.II rmail
To receive mail over \*(UU,
.B uuxqt
invokes the command
.BR rmail ,
which is a link to
.BR smail .
.B rmail
can also be another program that invokes
.B smail
directly as:
.DM
	smail -em -i -f\fIsender-address recipient address\fP ...
.DE
.PP
.II rsmtp
.II uux
An alternative method of receiving mail over \*(UU is through the command
.BR rsmtp ,
which receives batched SMTP requests.
This can be used between two sites running
.B smail
to gain many of the benefits of the SMTP protocol, such
as the ability to use recipient addresses that
.B uux
cannot correctly pass to a remote
.B rmail
program.
For example, an address that contains quotations
marks or spaces cannot be expected to pass correctly over an
.B uux-rmail
link, but will pass correctly over a
.B uux-rsmtp
link.
.SH "Addressing Under smail"
The following describes how
.B smail
interprets an E-mail address.
.PP
.B smail
understands domain-style addresses (e.g.,
.BR henry@mwc.com )
\*(UU-style path names, (e.g.,
.BR mwc!lepanto!henry ),
and local addresses (e.g.,
.BR henry ).
It assumes that an address of the form \fIuser\^\fB@\fIdomain\fR
is a domain address, that an address of the form
\fIhost\^\fB!\fIaddress\fR
is a \*(UU path, and anything else is a local address.
.PP
When it parses a mixed address (that is, an address that contains both a
`!' and a `@'),
.B smail
gives precedence to `@' over `!'.
Thus, it parses the address
.B a!b@c
as
.BR (a!b)@c ,
rather than
.BR a!(b@c) ,
which means that mail
addressed to
.B a!b@c
is forwarded to system
.B c
instead of to system
.BR a .
.SH "Resolving Addresses"
An E-mail address has two forms:
internal and external.
The internal form of an address is what appears on the
.B To:
line in the message's header.
This is the recipient's address as typed by the person who mailed the message.
This is regardless of whether the sender typed the recipient's
full address, or typed an alias for the recipient.
(For details on how to use aliases to address mail messages,
see the Lexicon entry for
.BR aliases .)
The external form of an address (also called the message's
.IR envelope ),
is the address that smail passes to the mail-delivery agent (either
.B uux
or
.BR lmail ).
.PP
Resolving is the act of transforming an internal address into an envelope.
It has two stages:
host resolution and alias resolution.
.II "routing^definition"
.I "Host resolution"
(also called
.IR routing )
is how
.B smail
figures out the identity of the computer to which it must send the message.
.II "alias resolution"
.II "alias expansion"
If
.B smail
determines that the message must be delivered on your local machine,
it then applies
.I "alias resolution"
(also called
.IR "alias expansion" )
to the address.
If the address proves to be an alias,
.B smail
expands the alias and again performs host resolution to find the machine to
which it should deliver the message.
If, however, the address names a user on your local machine, then
.B smail
hands the message to the local mailer
.B lmail
for delivery.
.PP
Although
.B smail
understands domain-style addresses (i.e., addresses that
contain a `@' and are read from right to left), it can deliver mail only to
\*(UU paths (i.e., addresses that contain `!' characters and are read from
left to right) and local addresses.
Thus, it must resolve a domain address into a \*(UU path or local address.
.PP
To resolve a domain-style address,
.B smail
must find the route to the most specific part of the domain,
as specified in the routing file
.BR /usr/lib/mail/paths .
Two degrees of resolution can occur:
.IP "\fBFull Resolution\fR"
.B smail
finds the full route to the machine.
In this case,
.B smail
either tacks the user specification onto the end of the machine's \*(UU path,
or resolves it into a local address, whichever is appropriate.
.IP "\fBPartial Resolution\fR"
.B smail
finds a route for only the right portion of the domain
specification; e.g., for
.DM
	henry@lepanto.mwc.com
.DE
.IP
it finds
.B mwc.com
but cannot identify
.BR lepanto .
Here,
.B smail
tacks the complete address (in the form
.BR domain!user )
onto the end of the \*(UU path.
For example, if
.B smail
finds that the route to
.B mwc.com
is via systems
.BR foo ,
.BR bar ,
and
.BR baz ,
it constructs the path:
.DM
	foo!bar!baz!lepanto.mwc.com!henry
.DE
.IP
This assumes that routing program on system
.B baz
(perhaps
.BR smail ,
perhaps some other program) will recognize the token
.B lepanto.mwc.com
as being a domain rather than a host.
.PP
It is an error to route a partially resolved address to the local host (a
null \*(UU path), because the local host is responsible for resolving the
address more fully.
.PP
The command-line option
.B \-r
tells
.B smail
to attempt to route the first (leftmost) component of a \*(UU path,
regardless of whether it knows how to
send mail directly to a site named further to the right in the path.
This is called
.IR "always routing" .
For example, if a mail message is address to
.DM
	foo!bar!baz!mwc!lepanto!fred
.DE
.PP
option
.B \-r
tells
.B smail
always to route the mail to
.BR foo ,
even if also knows how to route mail to
.BR mwc .
.PP
The command-line option
.B \-R
tells
.B smail
to route mail to the rightmost host named on a \*(UU path.
This is called
.IR "reroute routing" .
Use it if you have a very up-to-date routing table,
and wish to bypass some obsolete routing information in the current path.
.PP
If file
.B /usr/lib/mail/paths
does not contain a path to the remote system,
.B smail
forwards mail to the the host named in the entry
.B smart_path
in file
.BR /usr/lib/mail/config .
This lets your system depend on another, better
informed, system to deliver your mail.
Note that before you name another system as your system's
.BR smart_path ,
you should get the permission of the person who administers that system.
Please note that if you start to forward mail to a system without permission,
that system's administrator may forward your mail to the bit bucket.
.PP
After
.B smail
resolves an address, it reparses the address to see if it is now a \*(UU
path or local address.
If the new address turns out to be another domain address,
.B smail
complains.
This error occurs when an address partially resolves to the local host.
.PP
By default,
.B smail
does not alter an explicit \*(UU path of any mail message.
If the stated path is unusable (i.e., the next host is unknown), then
.B smail
applies always\-routing and attempts to deliver the message to first
(leftmost) system named in the \*(UU path.
If this fails,
.B smail
then uses reroute\-routing and again attempts to deliver the message.
If this too fails,
.B smail
finally attempts to to find a path to a smart-host and passes the mail to it.
And if that finally fails,
.B smail
mails an error message to user who mailed the message,
and abandons any further attempt to deliver the message.
.SH Headers
.II "RFC 822"
Document RFC822, which governs Internet mail, demands that a mail message
contain certain entries in its header.
These entries include one that begins with the string
.BR To: ,
one that begins with the string
.BR From: ,
and one that begins with the string
.BR Date .
If a message's header does not contain one or more of these entries,
.B smail
inserts it.
.SH "Build the From: Line of a Message"
The header of a mail message includes a line that begins
.BR From: .
This line names the user who originated the message.
This line is extremely important,
as it will read by users and programs on the recipient's system
to identify the sender, and possibly reply to the message.
.PP
.B smail
collapses the
.B From_
and
.B >From_
lines within a mail message to generate a simple ``from'' argument,
which it then uses to create its own
.B From:
line.
This processing sometimes is called
.I from-ming
a message.
The following gives the rules for from-ming:
.IP \(bu 0.3i
First, it concatenates all hosts named on remote from lines, separating
them from each other by `!'s.
.IP \(bu
It appends onto that concatenated address, the address from the last
.B From_
line.
.IP \(bu
If that address is in domain format
(i.e., the form \fIuser\^\fB@\fIdomain\fR),
.B smail
rewrites it in bang-path format (i.e., the form \fIdomain\^\fB!\fIuser\fR).
If a host or domain names the local system,
.B smail
ignores it.
.IP \(bu
Finally,
.B smail
removes redundant information from the
.B From_
line.
.PP
.B smail
generates its own
.B From_
line.
For mail that is to be forwarded via \*(UU,
.B smail
generates a line of the form remote-from host;
.I host
is the \*(UU host name (not the domain name), so that
.B From_
can indicate a valid \*(UU path, thus leaving the sender's domain address in
.BR From: .
.SH "Undeliverable Mail"
.B smail
returns to sender all mail that is undeliverable.
A message is declared to be undeliverable if the user is unknown,
or if the user resides on an unknown host.
.SH Logging
.B smail
uses two log files:
.IP \fB/usr/spool/smail/log/logfile\fR
The log of every mail message that your system receives.
Please note that if your system is busy, this file will quickly become
very large.
You should embed the command
.B /usr/lib/mail/savelog
in
.BR root 's
.B cron
file to ensure that this file is truncated and saved regularly.
For details on
.B savelog
or
.BR cron ,
see their articles in the Lexicon.
.IP \fB/usr/spool/smail/log/paniclog\fR
The log of every mail that created a panic situation.
If your system is configured properly, this file will never become large.
.SH "Registered Domains and Subdomains"
You may wish to register your domain with the NIC.
This will give you an internationally recognized e-mail address.
For more information, send E-mail to
.BR postmaster@internic.net .
.PP
Once you have registered your domain, you can also set up subdomains for
other systems, so they can receive information from the Internet
via your system.
The rest of this section discusses how to describe subdomains to
your system, and related topics.
.PP
Let's say that you have registered your domain, and you have named it
.BR mydomain .
To route mail systems subordinate to mydomain, do the following:
.IP \fB1.\fR
Insert the following entry into
.BR /usr/lib/mail/paths :
.DM
	.mydomain.com  %s 50
.DE
.IP
This tells
.B smail
that the local host (i.e., your machine) must resolve
that any address that ends in the suffix
.BR .mydomain.com ,
or it is an error.
.IP \fB2.\fR
For each site in
.BR mydomain ,
create two entries in
.BR /usr/lib/mail/paths .
For example, for the site
.BR foo.mydomain.com ,
create the entries:
.DM
	foo foo!%s  200
	foo.mydomain.com  foo!%s  200
.DE
.IP
If the site bar.mydomain.com is fed by the route
.BR froboz!florp!bar ,
insert these lines into
.BR paths :
.DM
	bar froboz!florp!bar!%s  200
	bar.mydomain.com  froboz!florp!bar!%s  200
.DE
.PP
Note that you do not have to register subdomains with the NIC.
Once you register the top-level domain with the NIC,
you control the entire name space \(em you can subdomain
to your heart's content.
.PP
The only restrictions on subdomaining may be with your Internet Nameserver.
.II "MX record"
Most nameservers for \*(UU domains publish a ``wildcard'' mail exchanger
(MX) record, that essentially says, ``send everything
for \fB*.mydomain.com\fR to this Internet gateway.''
However, some nameserver managers require you to register every site
in your domain, for which they provide a separate MX record.
The advantage of this scheme is that anybody on the Internet who sends
mail to your domain immediately receives an error message if the message
is addressed to a non-existent site.
For details, check with the person who manages your nameserver.
.PP
To route for an entire subdomain (e.g.,
.BR .subd.mydomain.com ),
you must choose a gateway for that domain (e.g.,
.BR gateway.subd.mydomain.com ),
and then use a line like this:
.DM
	.subd.mydomain.com gateway!%s  200
.DE
.PP
.B smail
automatically chooses the longest subdomain match it can find, so
this rule applies before the
.B .mydomain.com
.B %s
rule.
.PP
Note that the gateway need not be in the subdomain itself.
You could have a line elsewhere in the
.B paths
file on
.B mydomain
that says:
.DM
	gateway.mydomain.com  gateway!%s  200
.DE
.PP
Your main gateway may also have information about machines in subdomains,
although this is not necessary.
For instance, if your main machine is
directly connected to a machine in a subdomain, you may want to put this
information into
.BR paths ,
so the mail will not go through the gateway for that domain.
.PP
For example, the machine
.B smith.subd.mydomain.com
might be directly connected to your master gateway,
.BR mydomain.com :
.DM
	smith  smith!%s  200
	smith.subd.mydomain.com smith!%s  200
.DE
.PP
Without this rule, mail for
.B smith
would be queued for forwarding through
.BR gateway.subd.mydomain.com .
.SH "Compatibility With sendmail"
.B smail
was designed to be a plug-in replacement for the BSD program
.BR sendmail ,
in that external programs can call
.B smail
in the same way that they call
.B sendmail
and expect similar results.
However,
.B smail
is completely different internally and has entirely different configuration
files.
As a result, the option
.B \-o
to
.B smail
only sets a few configuration parameters that were believed
to be commonly used by other programs.
Also, for convenience, some new (upper-case only) parameters
are defined only in
.BR smail .
.B smail
ignores attempts to use this flag to set other options.
For a complete list of the
.B \-o
options that
.B smail
recognizes, see the section on command-line options, above.
.PP
.II /usr/lib/sendmail
.II sendmail
For compatibility with other software systems (in particular, the Taylor
\*(UU package), \*(CO links
.B smail
to command
.BR /usr/lib/sendmail .
Thus, a program that expects to use
.B sendmail
can use
.B smail
without being recompiled or reconfigured.
.SH "Configuration Files"
For most sites, the configuration compiled into
.B smail
is sufficient, and thus no configuration files are needed.
However, you can use any or all of
the following optional configuration files to restructure how
.B smail
behaves on your system:
.IP \fB/usr/lib/mail/config\fR
General configuration.
This file can override compiled-in configuration,
including the names of any of the following configuration files.
.IP \fB/usr/lib/mail/directors\fR
Configuration file for
.B smail
directors, i.e., configured methods for resolving local addresses.
.IP \fB/usr/lib/mail/routers\fR
Configuration file for
.B smail
routers, i.e., configured methods for resolving or routing to remote hosts.
.IP \fB/usr/lib/mail/transports\fR
Configuration for
.B smail
transports, i.e., configured methods of mail delivery.
.PP
The contents of file
.B config
dictate how
.B smail
configures its internal workings \(em where it looks to find
other configuration files, where it should send error messages, and so on.
The contents of
.BR routers ,
.BR directors ,
and
.B transports
together tell
.B smail
how to deliver mail both on your local system and on remote systems.
The following describes how these files work together.
.PP
When
.B smail
is given a list of addresses to which a message is to be
delivered, it processes the list iteratively until it produces a list of
resolved addresses.
When an address is resolved,
.B smail
will know which transport it must use to deliver the message
to the person or persons to whom it is addressed,
and all data that this transport requires.
To accomplish this, smail goes through the following steps:
.IP \fBA.\fR 0.3i
.B smail
first parses each address to find a host name, called the
.IR target ,
and the remaining part of the address, called the
.IR remainder .
.IP
As a simple example, in the address
.BR tron@uts.amdahl.com ,
the host part
.B uts.amdahl.com
is the target and
.B tron
is the remainder.
Likewise, in the address
.BR sun!amdahl!tron ,
the target is
.B sun
and the remainder is
.BR amdahl!tron .
.IP \fBB.\fR
.B smail
then shows each address to directors,
in the order given in file
.BR /usr/lib/mail/directors ,
until one of the directors says that it knows what to do with that address.
That director can either return a new
list of addresses, or put the address onto a list of resolved addresses.
If new addresses are produced,
.B smail
places them onto the input list, to be processed from step
.BR A .
.IP \fBC.\fR
When an address has passed through step
.BR B ,
.B smail
shows it to various routers,
in the order given in file
.BR /usr/lib/mail/routers ,
until a router can match the target name for the address.
If no router can
match the complete target, then
.B smail
selects the router that matches the longest portion of the target.
The router names the transport to be
used to deliver the message to that address, plus some other information
that the transport requires (e.g., the next host and next address values).
The information as to which transport to use can come either
from the definition of the router, from a method file, or may be
specified by the router specifically.
.PP
When all addresses have been resolved,
.B smail
sorts them and passes them to transports.
The transport then delivers the message to the addresses it is given.
.PP
Host names and local user-names are matched independent of case; for
example, ``Postmaster'', ``POSTMASTER'', and ``postmaster'' are in effect
all the same.
In addition,
.B smail
keeps an internal hash table of all regular recipient addresses,
that is, all addresses that do not specify files or shell commands.
This table is used to discard duplicate regular recipient addresses.
This hash table is independent of case, as well, so
that the address
.B Postmaster@SRI-NIC.ARPA
is considered a duplicate of
.BR postmaster@sri-nic.arpa .
.SH "Other Files and Directories"
.B smail
also uses the following configuration files:
.IP \fB/usr/lib/mail/qualify\fR
Configuration file for host-name qualification.
.IS \fB/usr/lib/mail/retry\fR
Optional delivery retry configuration file, i.e., minimum time between
retries and maximum time to retry before giving up.
.PP
.B smail
reads the following files to learn how to redirect mail locally and to give
paths to remote sites:
.IP \fB/usr/lib/mail/aliases\fR
Aliases for mail addresses.
.IS \fB/usr/lib/mail/paths\fR
Paths to remote hosts.
.IS \fB/usr/lib/mail/lists\fR
Mailing-list files.
.IS \fB/usr/spool/mail\fR
The directory that holds each user's mailbox file.
.IS \fB$HOME/.forward\fR
Forwarding address or addresses for a given user.
.PP
.B smail
uses the following directories to hold incoming mail messages and its
work files:
.IP \fB/usr/spool/smail\fR
Directory that holds spool directories and work files.
.IS \fB/usr/spool/smail/input\fR
Spool directory for incoming messages.
.IS \fB/usr/spool/smail/error\fR
Directory that holds mail messages that failed for a reason that the
site administrator should investigate.
.IS \fB/usr/spool/smail/msglog\fR
Directory that holds transaction logs for individual messages.
.IS \fB/usr/spool/smail/lock\fR
This directory holds 
.BR smail 's
input lock files.
.PP
The following files log 
.BR smail 's
activity.
Please note that these files will grow without end.
Your system's system administrator should check and
truncate these files from time to time.
She can also use the script
.B /usr/lib/mail/savelog
to manage these files; for details, see the Lexicon
entry for this command:
.IP \fB/usr/spool/smail/log/logfile\fR
A log of 
.BR smail 's
transactions.
.IS \fB/usr/spool/smail/log/paniclog\fR
A log of configuration or system errors encountered by
.BR smail .
.SH "See Also"
.Xr "commands," commands
.Xr "mail [command]," mail.c
.Xr "mail [overview]," mail.o
.Xr "mailq," mailq
.Xr "rmail," rmail
.Xr "rsmtp," rsmtp
.Xr "runq," runq
.Xr "savelog," savelog
.Xr "smtpd" smtpd
.SH Diagnostics
If all goes well,
.B smail
returns zero to the shell when it exits.
If an error occurs, it returns a value other than zero.
The meaning of each code is set in 
.BR smail 's
source file
.BR exitcodes.h ,
as follows:
.LB
\fBEX_USAGE\fR	Error in command-line usage
\fBEX_DATAERR\fR	Data-format error
\fBEX_NOINPUT\fR	Cannot open input file
\fBEX_NOUSER\fR	Addressee unknown
\fBEX_NOHOST\fR	Host unknown
\fBEX_UNAVAILABLE\fR	Service unavailable
\fBEX_SOFTWARE\fR	Internal software error
\fBEX_OSERR\fR	System error
\fBEX_OSFILE\fR	Critical OS file missing
\fBEX_CANTCREAT\fR	Cannot create (user) output file
\fBEX_IOERR\fR	Error in file I/O
\fBEX_TEMPFAIL\fR	Temporary failure; user can retry
\fBEX_PROTOCOL\fR	Remote error in protocol
\fBEX_NOPERM\fR	Permission denied
.PP
If you invoke
.B smail
with its option
.BR -bd ,
then the message
.DM
	bind() failed: address already in use
.DE
.PP
means that another process is already listening to the SMTP socket.
.SH Notes
Many mail bugs are not
.B smail
bugs.
.B smail
cannot help it if remote sites trash your mail messages.
.PP
Setting the input spool directory processing interval to a period of more
than 2,147,483,647 seconds will result in an incorrectly calculated
processing interval \(em and is a rather silly thing to do at any event.
.PP
Copyright \(co 1987, 1988 Ronald S. Karr and Landon Curt Noll.
Copyright \(co 1992 Ronald S. Karr.
.PP
For details on the distribution rights and restrictions associated with
this software, see file
.BR COPYING ,
which is included with the source code to the
.B smail
system; or type the command:
.DM
	smail -bc.
.DE
