sendmail.m4 - Introduction to using m4 macros to create a
sendmail.cf configuration file
The following list provides definitions of the operands
used in the configuration files. The operands appear in
the recommended usage order. This macro specifies the
name of the next-highest domain above your own (yyy.xxx).
It is used to determine which hosts you can send mail to
that might be close enough to be reached directly, and to
figure out where MyDomains are located. This macro specifies
the list of all the domains under ParentDomain that
are aliases for your own. It is a list of single tokens
separated with blanks. These are qualified under ParentDomain
in actual use. You must include the single-token
component of MyDomain. For example, if the ParentDomain
is ECD.COM and MyDomain is AP.ECD.COM, then MyDomains must
include at least the token AP. This operand is used in
conjunction with the _MailHub operand. This macro specifies
the fully-qualified domain that you are in. It must
end in _ParentDomain.
If you set both MyDomain and ParentDomain to the
string LOCAL, sendmail assumes that you do not have
a domain, but instead use single-token hostnames
(which can include dashes and underscores but not
dots) and that you are using /etc/hosts or NIS, but
not BIND. This macro is used to initialize the $=w
operand. If your host is known by several names
inside of _MyDomain, you must put the first token
of all names (optionally including the first token
of your /bin/hostname) into this list.
In a TruCluster Server cluster, you should also
specify the cluster alias and the unqualified hostnames
of all the members of the cluster. This
macro specifies the domain name (@DOMAIN) appended
to any mail address that leaves the local domain
and does not have a domain name in its address.
(For example, local user names do not have the
domain name in the address.)
Usually, _MyDomain is specified; therefore, the
mail leaves the domain with a host name (such as,
[email protected]) even though there is no such
host.
If you do this, you need an MX RR at the root ("@")
of the domain that points to some set of mail
servers whose MyDomain's variables include your
domain. This is irrelevant if you are using LOCAL
for MyDomain and ParentDomain. Use this macro if
you are using rdist, or NIS to ensure that all
aliases on all machines in your local domain are
equivalent. (They do not need to have the same
values, but the same alias names must be present on
all machines.)
Note
It is recommended that you use this macro, unless
you have specific reasons for not using it.
If you use this macro, mail sent to @MyDomain is
treated as local mail, which means that any host in
the domain can strip off the @MyDomain and search
its aliases database to decide what to do with the
message.
Mail sent to other hosts in the local domain with
MailCluster turned on will have the hostname
(rather than ExportedName) appended to the username.
Because it is local mail, you know it came
from some host in the local domain and you presumably
want to know which host.
Note
Setting ExportedName to MyDomain and turning on
MailCluster, creates an environment where all mail
names are equivalent on all hosts in the domain.
This simplifies the address formats for all local
mail. You use this macro if your machine recognizes
mail to user@localdomain and therefore can
access anyone's mailbox (usually through an aliases
file containing the real mailboxes for everyone who
might receive such mail). A Mail Hub treats all
mail to user@localdomain as local mail by using the
aliases file.
This is different than a Mail Cluster, where every
host acts as a Mail Hub (by virtue of everyone having
the same "all knowing" aliases file). This
macro specifies the mail spool location (which is
usually /var/spool/mqueue). Note that there is no
advantage to using /usr/spool/mail for this if that
is a symlink to /var/spool/mail. Using the correct
names and avoiding symlinks is recommended. This
macro specifies the list of user names that are
allowed to run sendmail with the -f option that
sets the envelope sender address. There are users
that have a legitimate need to use the -f; however,
for security reasons, it is recommended that only
those users be allowed that option. This macro
specifies the list of users that have the @hostname
of the sending host added to their From: line, if
they send mail to some other host in the local
domain. This procedure is performed regardless of
the MailCluster and MailHub. This macro sets the
unqualified hostname.
This macro is not required. Under Tru64 UNIX sendmail
it is recommended that you do not use this
operand. This macro enables your machine to recognize
POP customers as username.POP. This is
preferable to HostPOP. as shown in the following
example. If you use this macro, you must format
your aliases as follows: username:username.POP
Instead of the following format: username:username@POP
Be aware that older versions of the popaka utility
create the @pop style address. If you want to
change, turn both TagPOP and HostPOP on and wait
for a new popaka utility, at which point you can
shut off HostPOP. This macro enables your system
to be able to recognize IMAP customers as username@IMAP.
Older popaka utilities generate aliases
in this form. If you are using an older version of
the popaka utilities, you can enable HostIMAP. However,
you will not be able to name any host in your
domain "IMAP" because it would conflict with the
sendmail.cf file's internal meaning for the @IMAP
string. It is recommend that you use TagIMAP.
This macro enables you to recognize DECnet-style
addresses or to communicate with DECnet. This
macro only applies to DECnet. You use this macro to
define this to your DECnet node name if your sendmail
binary does not define $=y as the result of
DECnet's getnodename() call. If you have such a
binary, it is best not to define this variable
because that way you can share a single sendmail.cf
file across all of your DECnet nodes. Otherwise
you need to build a separate sendmail configuration
file for DECnet node, just to set $=y. Tru64 UNIX
automatically defines $=y if DECnet's installed.
This macro applies to DECnet only. You can use
this macro, if you are using the UTK Mail11 package.
This macro enables your system to recognize
UUCP addresses. If you do not also define _GateUUCP,
you must run UUCP on your host. In most
cases, mail with UUCP addresses is relayed to a
host that recognizes UUCP addresses to process the
address. This macro enables your system to recognize
POP customers. This macro instructs sendmail
to format your headers in RFC 976 format. For example:
From: [email protected] (Paul Waxie)
If you use this macro, you should define this to be
T. These macros control how mail that is destined
for some other host in your local domain is handled.
TransDomain is the transport used to reach other
hosts or to reach the designated gateway (usually
smtpl which specifies local SMTP).
If you decide to route all such local-domain mail
through a gateway, then specify the name of the
gateway in GateDomain. If you want the mail to go
directly to the gateway, do not specify anything
for the GateDomain operand.
In practice, TransDomain is always set to smtpl and
GateDomain is always either null or the name of
your local mail hub. However, there is no penalty
for sending local mail directly between workstations
and no advantage for sending such mail
through your mail hub. Using a gateway is not recommended
for local mail. These two macros perform
the same functions as TransDomain and GateDomain
except that they control mail which is sent to the
parent domain rather than to the local domain.
In most domains, there are no security filters that
restrict SMTP traffic between hosts in the domain.
If that is true in your domain then it is
recommended that you set TransParent to smtp and
set GateParent to null string.
As with local-domain mail, there is no real advantage
to using a gateway for local mail. These
macros specify the transport to be used and the
gateway host for mail leaving the domain.
If you are directly connected to the Internet, then
you can set TransINET to smtp and leave GateINET
empty.
If you need to use a gateway to reach the Internet,
then set TransINET to the protocol used by the
gateway (uucp, mail11, or smtp) and set GateINET to
the name of the host you will reach through that
transport. That host will presumably deliver your
mail to its ultimate recipient or forward it to
another host that will deliver the mail or forward
it on.
If you leave GateINET empty, then TransINET is
ignored because it must be the local smtp transport.
These macros specify the transport and the
gateway for UUCP mail. Note that if GateUUCP is
empty, then TransUUCP is ignored since the local
uucp transport must be used. In which case uux is
used as the transport.
You might set TransUUCP to smtpr. GateUUCP host
has aliases for all of your users. This permits
outbound UUCP addresses to omit your local host
name. This macro specifies the UUCP host name for
all of the members of your TruCluster Server cluster
running the UUCP protocol. Use this macro if
you are running UUCP on your system. See protocols.map(4) for more information. This macro specifies
the arguments for UUCP. For a complete list
of the possible options, see uux(1). This macro
specifies the name of a host on your network that
is capable of accepting mail sent to the USENET.
If there is no such host on your network, leave
this macro empty.
Note that Tru64 UNIX does not currently include the
software necessary on the receiving host, because
it varies according to whether you are running C
News or B News or INN. This macro applies to DECnet
mail only. If your users or your inbound
mail11 listener puts a pseudodomain name other than
on incoming addresses, sendmail needs to know.
This macro applies to DECnet only.
If GateIV is set to an empty string, then sendmail
attempts to deliver the mail directly using TransIV
(which is almost always smtp).
If you have MX RRs for all of your mail11 hosts
then you can use SMTP to reach them or at least the
closest relay host.
If GateIV is set to a fully qualified host name,
then TransIV is used to forward the mail to that
host, unless GateIV is set to the same hostname.
In this case the mail11 mailer is called directly.
This lets you share a sendmail.cf file across all
of your workstations and mail11 gateway machines,
because the mail will go to the designated mail11
gateway first, which, on forwarding, the mail will
recognize its own name as the designated gateway
and instead call the mail11 transport.
It is recommended that you set TransIV to smtpr if
the GateIV host has aliases for all of your users.
This enables outbound DECnet addresses to omit the
local host name. This macro applies to DECnet
only.
Mail from a DECnet node is always encapsulated in a
pseudodomain. The DECnet pseudodomain is an arbitrary
string that should be used uniformly by your
site or organization. The DECnet pseudodomain must
always appear after the parent domain. For example,
in the following domain name, QNET is the DECnet
pseudodomain portion of the domain names:
NODEONE.QNET.ECD.COM
NODETWO.QNET.ECD.COM
PhaseIVdomain is the non-qualified name of the
pseudodomain. It is always qualified with ParentDomain
before being emitted into the Internet.
This can be anything you want but is usually the
name of the DECnet network. Do not set this to
DNET. Set it to the proper name of your network,
not the name of the network's technology. This
macro specifies the Phase IV node names of the
nodes in your TruCluster Server cluster. Use this
macro only if your node is running DECnet. This
macro specifies the Phase IV node address. Use this
macro only if your node is running DECnet. This
macro applies to DECnet only.
This macro specifies the location of the mail11
binary. For this operating system it is located in
/usr/sbin/mail11v3. This macro applies to DECnet
only.
Unnamed DECnet nodes are reachable through the
AA.NNN:: notation. The AA in this case is actually
of higher precedence than the NNN. You may want to
reverse the order when rewriting into Internet form
because Internet addresses have higher precedence
toward the right side. Whatever you do, you must do
it consistently across all mail11 gateways in your
network, and you will probably not be able to
change your mind later. This macro applies to DECnet
only.
This macro applies to DECnet Phase V only. It
specifies the namespace that sendmail assumes for
any mail it receives in without a namespace, if you
are running DECnet Phase V. It is recommended that
you make it the name of the namespace you are in.
If you are running DECnet Phase IV, you must get
the name of the namespace from your network administrator.
These macros apply to DECnet Phase V
only. They specify the transport, gateway, and
pseudodomain for DECnet Phase V mail.
Note that Phase V names are always reversed so
there is no ReversePhaseV variable. This macro
specifies the Phase V node names of the nodes in
your TruCluster Server cluster. Use this macro only
if your node is running DECnet. This macro enables
your system to MR or UMC addresses. If you do not
define GateMsgRout you must run UMC on your host.
Most hosts use a gateway to reach MR. This macro
applies to DEC MessageRouter (mail-plus) only. They
define the transport, gateway, and pseudodomain.
This macro applies to the DEC MessageRouter (mailplus)
only. It specifies other pseudodomains that
the software or your users may use, expecting them
to be recognized as Message Router pseudodomains.
Use this macro if you have an IDA version of sendmail.
This turns on split rewrite rules (O/). It
also allows for local aliases lookup. If you are
usingTru64 UNIX's sendmail utility, it is recommended
that you set this operand to be T. This
macro specifies that aliases in your local aliases
file are _NonHiddenUsers. You must have _IDA
defined because it uses IDA features to do the
aliases lookup. See the explanation of _NonHiddenUsers
and _IDA. This macro specifies to bypass
most of the other routing options (for example,
GateDomain) and forces your mail to be sent by
_TransINET to your _GateINET machine. This allows
workstations with simple mail configurations to
create mail locally, but have it appear as if it
came from the main relay (GateINET) machine. Using
this option can simplify things for the system
administrator, by funneling all mail through central,
well-maintained machines.
The only mail that is delivered locally (to the
simple workstation) is the mail addressed to the
user names contained in _NonHiddenUsers. This
macro enables sendmail to work in a TruCluster
Server cluster environment. Set it to T if your
system is part of a cluster. This macro specifies
the alias for your TruCluster Server cluster. Use
it only if your system is configured as part of a
cluster. This macro specifies the unqualified
names of the nodes in your TruCluster Server cluster
that can handle X.25 (PSI) mail. Use this macro
only if you are running X.25 on your system. This
macro specifies that sendmail will use an LDAP
server to resolve aliases. If you intend to use
LDAP, set this macro to T. See Lightweight Directory
Access Protocol for more information. This
macro defines the map type and LDAP search string
for sendmail to specify when it contacts an LDAP
server for alias resolution. The map type is
ldapx.
The sendmail command supports most of the standard
map options as well as options specific to LDAP.
The following LDAP options are the ones most users
need, but you can specify additional parameters
depending on your application.
You must specify arguments for each LDAP option as
strings, therefore, you must enclose the arguments
in double quotes ("). Also, the arguments must
immediately follow the associated LDAP option, that
is, leave no space between options and double
quotes. LDAP base Distinguished Name (DN) search
string LDAP server's host name list. This contains
the list of server names to use for an LDAP search.
The list of names is separated by white space.
String containing a list of attribute/value pairs
for which to search in the LDAP database. The syntax
for each pair is attribute=%s, where %s is the
token for which to search.
If you need to specify more than one
attribute/value pair, you must enclose each pair in
parentheses (). In addition, you must begin the
string with (|). For example:
"(|)(attr1=%s)(attr2=%s)(...)(attrN=%s)"
You can specify up to 1024 attribute/value pairs.
String containing a list of comma-separated
attributes for which to return values. For each
LDAP record that matches the attribute/value pairs
you specify in the -k option, the LDAP server
returns the corresponding attribute you specify
with the -v option.
The brackets {} are necessary to tell the m4 command
to treat the double quotes as literal; otherwise,
the quotes are not preserved in the sendmail.cf
output file.
For example, assume your LDAP base DN is compaq,
your LDAP server name is ldap.site.com, the search
attribute is mailaddr, and the return attribute is
forwardAddr. You would specify the _LDAPParam macro
as follows (the backslash indicates line continuation):
define(_LDAPParam, {ldapx -b"o=compaq"
-h"ldap.site.com" \
-k"(mailaddr=%s)" -v{"forwardAddr"}})dnl
The mailsetup script enables you to create new mail configurations.
If you have experience creating sendmail.cf
configuration files or your system requires specialized
configuration files, you might want to create your configuration
files manually.
Use the macros described in this reference page to generate
a configuration file. You should save your configuration
file under the name hostname.m4, where hostname is
the name of your system or the alias for a TruCluster
Server cluster.
After you create the m4 file with the operands you need,
you can generate the sendmail.cf file by issuing the following
command: # m4 -D_Configfile=hostname.m4 sendmail m4
> sendmail.cf
You must be in the /var/adm/sendmail directory to use this
command.
The sendmail.m4 package used byTru64 UNIX provides the
following functions: Rewrites addresses, encapsulating
mail from non-Internet protocols (for example, DECnet)
within pseudodomains. This helps to ensure that replies
are sent back to the correct address, where they can be
handled appropriately. Performs routing, based on the
domain to which the mail is sent. Supports multiple
return address formats, including domain-based addresses.
For example, a host with the name myhost.mysite.ecd.com
would normally format a user's mail address as
[email protected], or user@cluster_alias.mysite.ecd.com
in a TruCluster Server cluster
(which changes the address only for SMTP). By using the
_ExportedName operand, you can set the return address to
be mysite.ecd.com. By using the _MailHub and MyDomain
operands, your mail system recognizes the phrase
mysite.ecd.com as a synonym for this host.
The dnl command is "delete to newline" command and causes
the m4 compiler to ignore the dnl characters and all text
that follows it, up to and including the end of line. If
you do not follow a define command with a dnl command,
then the newline after the right parenthesis ()) is emitted
into the output (which is a sendmail.cf file).
Blank lines are permitted in the sendmail.cf file; however,
they are unnecessary and not recommended.
Braces ({}) are used as quoting characters. You can use
them even when they are not required.
Note that null definitions have the following of the form:
define(Operand, {})
The only rule you must follow in creating the configuration
m4 file is to surround literal text with braces ({});
however, you must leave macro names (which you presumably
want expanded by m4) unquoted. (That is, do not enclose
macros that you want expanded in braces ({}).)
Mailers [Toc] [Back]
The sendmail program invokes a mailer to handle your mail.
Usually, this is local (for local delivery on the host),
smtp (standard SMTP), smtpl (SMTP local), or smtpr (SMTP
to relay) for delivery over the Internet. These mailers
(smtp, smtpl, and smtpr) invoke SMTP to deliver the mail;
however, they differ in how they rewrite the return
address. If you are in doubt as to which mailer to use,
it is safest to use smtp.
The smtp mailer qualifies your mail with the ExportedName
operand, except for mail sent from NonHiddenUsers or from
an alias (if AliasesLocal is true).
The smtpl mailer handles mail sent within you local
domain. This mailer is used when mail is sent to users
within the local domain. Depending on how the _MailCluster
and _NonHiddenUsers operands are defined, the hostname is
removed from the return address before the mail is sent.
The smtpr mailer always removes the hostname, except for
_NonHiddenUsers. This is useful when the relay machine is
a mail hub and has aliases for all users in your mail system.
Routing [Toc] [Back]
The sendmail.m4 package performs some routing decisions
based on the domain in which the address ends. In general,
you can configure your system to check for some special
cases (for example, DECnet or UUCP style addresses).
If the address does not conform to any of the cases specified,
it will check to see if the mail resides in your
local domain (_GateLocal), parent domain (GateParent), or
is outside your local network (GateINET). You can configure
your system to pass mail to and from the Internet by
setting the _GateINET operand to the name of the Internet
gateway on your local network and leaving the GateDomain
and GateParent operands blank.
Lightweight Directory Access Protocol [Toc] [Back]
The sendmail command supports the Lightweight Directory
Access Protocol (LDAP) for alias resolution. LDAP is an
open protocol for accessing directory services. An LDAP
server provides information, such as email addresses and
public keys, to applications running on client systems.
Usually, when sendmail parses a recipient's address and
determines that the address is local, it looks up the
address to determine if there are any aliases associated
with it (see aliases(4)). If sendmail does not find an
alias, it looks in the file in the recipient's home directory
to see if the recipient has any personal aliases.
While this works well for a single system, it becomes cumbersome
to maintain in a distributed environment. Performance
suffers if the list of aliases becomes too large.
With LDAP as another means for storing user alias information,
sendmail can share aliases in a distributed fashion,
and as a result, system administrators do not have to
maintain several databases. Furthermore, because there are
fewer databases and the LDAP servers that serve them are
typically dedicated machines, address resolution is more
efficient. (Note that the sendmail command itself requires
a fair amount of resources, and performing alias resolution
on the same system can be costly.)
To configure sendmail with LDAP, set the _LDAPMap operand
to {T} and specify the LDAP search string in the _LDAPParam
operand. The appropriate map line and rules are added
to the system sendmail.cf file. This tells sendmail to
perform an LDAP lookup for the receipient's address in
addition to the standard alias and lookup. If no matches
are found, the recipient address is considered to be local
to this system.
sendmail.m4(8)
[ Back ] |
