InfoMagic Internet Tools 1993 July/Internet Tools.iso/RockRidge/mail/sendmail/uk-sendmail2.1/Docs/Tutorial.ms

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.TL
Sendmail Configuration Package UK-2.1
.sp
A Tutorial based on the Examples
.AU
Jim Crammond
.AI
Dept of Computing, Imperial College,
University of London, England
.AU
Jem Taylor
.AI
Dept of Computing Science,
University of Glasgow, Glasgow, Scotland
.DA 27 November 1988
.LP
.NH
Setup at the example site cs.glasgow.ac.uk
.LP
The site
.I cs.glasgow.ac.uk
has several dozen machines using the
generic
configuration 'slave' and two machines 'gateway' and 'uurelay' which
have configurations of their own.
We also generate configurations for two other
glasgow sites which are each set up in a similar way.
This database of domain and channel
tables is therefore used to make a total of five different configurations.
Tables basically fall into three categories:
.DS L
Tables used in all configurations (with prefix "glasgow.")
Tables used in cs dept. configurations (with prefix "cs-dept.")
Tables used in only one configuration (e.g. with prefix "uurelay.")
.DE
.LP
These tables can be found in the Examples directory.
The following notes will cover the three configurations used for
.I cs.glasgow.ac.uk.
The arrangement of data files also takes account of other configurations
generated from them for other sites.
.LP
All users have entries in
.I /usr/lib/aliases
which is maintained centrally on the host that has the master copy of
.I /etc/passwd
and we ensure that all our users have accounts on that machine, though many have
.I /bin/noaccount
as their login shell.
.KS
.NH
Site topology
.DS I

 -
 |
 |-- gateway (janet relay, sendmail database master & alias database master)
 |        +---> janet WAN including relays to overseas domains
 |
 |--
 e
 t--
 h
 e-- (dozens of) 'slave's
 r
 n--
 e
 t--
 |
 |
 |-- uurelay (uucp relay & news)
 |       +---> uucp neighbours
 -

.DE
.'have to use a vertical backbone so that troff can draw the diagram properly.
.KE
.NH
The generic configuration 'slave'
.LP
The
.I slave
configuration is used on all machines which have only an ethernet connection.
This includes two sun fileservers and their clients.
The client workstations all mount /usr/spool/mail from
their respective servers. Users with mailboxes on these machines have
entries in /usr/lib/aliases pointing to the fileservers so that
mail delivery is always done by the server.
.SH
Note
.IP
This is only safe if the NFS implementation supports flock() properly, as
SUNs after version 3.4 SunOS, and 4.3BSD systems appear to do. Check your
documentation.
.LP
The configuration itself is quite minimal, containing enough information
to send mail directly to internal hosts but passing all "unknown" addresses
to 'gateway' to resolve.
.LP
.KS
.NH 2
The configuration description 'config.slave'
.DS I
# basic settings
config=slave
domain="cs.glasgow.ac.uk"
options=multihost,nrsformat
postmaster=mailer-daemon
tabledir=tables

# domain tables
domain std file="cs-dept.ether.chn"
domain top file="slave.top.dom"

# channels
channel top file="slave.top.chn"
channel local file="cs-dept.local.chn",
        showldomain,shownrs,showuucp
channel ether file="cs-dept.ether.chn"
channel ether file="cs-dept.uucp.chn"
channel news file="cs-dept.news.chn",relayed
.DE
.KE
.LP
Taking the lines one by one:
.SH
config=slave
.LP
The name of the configuration is 'slave'.
The result of running 'make' will be a file named 'slave.cf'.
.SH
domain="cs.glasgow.ac.uk"
.LP
The domain name of the site is
.I "cs.glasgow.ac.uk" .
Unless otherwise specified, mail leaving the site will be marked
.I "From: [e-mail]" .
.SH
options=multihost,nrsformat
.LP
The configuration is for a 'multihost' site - more than one host will
show itself to the outside world with the same site domain name.
The host specific domain name is `hostname`.cs.glasgow.ac.uk
but no-one outside the site will be aware of it.
.LP
The configuration will recognise addresses with domains in the JNT
sponsored NRS domain order - e.g.
.I [e-mail] .
.SH
postmaster=mailer-daemon
.LP
When sending error messages, sendmail will stamp them
.I "From: mailer-daemon" .
To prevent error loops, messages
.I "To: mailer-daemon"
should not be allowed to cause error messages themselves.
There must therefore be an alias in
.I /usr/lib/aliases
to send such mail to someone.
.SH
tabledir=tables
.LP
We keep the domain and channel tables for all configurations in one
directory called "tables" - you will find this directory in the Examples
directory.
.SH
domain std file="cs-dept.ether.chn"
.LP
The list of domains for local hosts are stored in this file (named relative
to tabledir).
Note that the same file is also used for the ether channel, since all local
hosts are directly reachable on the ethernet.
.SH
domain top file="slave.top.dom"
.LP
This contains the top domain data. In fact it contains just the one line
.DS
uk
.DE
.LP
since these machines send all mail that they cannot deliver to 'gateway'.
.SH
channel top file="slave.top.chn"
.LP
This file contains the one line
.DS
ALL    gateway.cs.glasgow.ac.uk
.DE
.LP
which sends all unrecognised domains to the domain
.I "gateway.cs.glasgow.ac.uk" ,
for which there is an entry in
.I cs-dept.ether.chn .
The domain recognition is thus centralised on the machine 'gateway',
with slave machines only containing local information.
.LP
The advantage of doing this is that the slave configuration only needs
to be updated when new machines arrive (or disappear) locally on the
ethernet. The disadvantage is that the slaves can not recognise obvious
mistakes in addresses - all rubbish will be sent to 'gateway' where it
gets rejected.
.SH
channel local file="cs-dept.local.chn", showldomain, shownrs, showuucp
.LP
This file contains the site domain name and host specific domain name, thus:
.DS
cs.glasgow.ac.uk
LHOST.cs.glasgow.ac.uk
.DE
.LP
Since this file is shared with other configurations, it also contains some
obselete names which still occur from time to time (e.g.
.I glasgow.uucp ).
.LP
Some channel-specific options are specified:
.I 'showldomain'
causes the local site domain name to be put on messages sent locally,
so that mail from another user is delivered with
.I "From: [e-mail]"
rather than
.I "From: user" ;
.I 'shownrs'
causes message headers to have NRS domain order, so that the message is in
fact delivered with
.I "From: [e-mail]" ;
.I 'showuucp'
uses a heuristic to detect uucp style paths in headers. If an address
contains several one-word site names, it is presented as a uucp style bang
path, so that e.g.
.IP
From: bill%tipsy%mumps@illvax
.LP
will be re-written as
.IP
From: illvax!mumps!tipsy!bill
.SH
channel ether file="cs-dept.ether.chn"
.LP
The domains listed in this file are accessible by ethernet.
This is the same file as is used for internal domain data above.
.SH
channel ether file="cs-dept.uucp.chn"
.LP
We have a second ether channel table containing those few NRS names
which are actually uucp sites connected to uurelay. These contain
the domain name of the uucp site and 'uurelay' as the host to send to.
.SH
channel news file="cs-dept.news.chn",relayed
.LP
The "usernames" described in this file are taken to represent newsgroup names,
so that (for example) mail which
is addressed to a local user called "comp.mail.sendmail" is sent to the
news channel. Since there are hundreds of newsgroups, we use wildcards
to match just the top level newsgroup names, e.g.
.DS
comp.%s    uurelay
.DE
.LP
The
.I 'relayed'
option indicates that
.I mail-news
is to be invoked on a different host, in this case 'uurelay'.
We run news on 'uurelay' and mount its /usr/spool/news filesystem on all
the other hosts using NFS (mounted soft,read-only to prevent hanging).
On all the other machines
.I inews(1)
is a shell script containing
.DS I
#!/bin/sh
/usr/hosts/uurelay $0 $@
.DE
.NH 2
Installing the configuration file
.LP
Since this is a shared configuration, we have a shell script to
call the program
.I Install.sh
for each 'slave' host.  In the case of the sun fileservers, Install.sh
is invoked with the -f option that prevents a freeze file
(/usr/lib/sendmail.fc) from being created; on the client machines we only
wish to restart the daemons, so we use the -n option, thus we have:
.DS I
sh Install.sh -f sun1 slave.cf
sh Install.sh -n sun2 slave.cf
sh Install.sh -n sun3 slave.cf
etc . . .
.DE
.NH 2
Shared system mailboxes
.LP
As mentioned above, the client workstations mount /usr/spool/mail from
their NFS fileservers. At glasgow we go one stage further and only run
sendmail SMTP listeners on the servers.
Sendmail daemons on the client machines are started with
.DS
/usr/lib/sendmail -q1h
.DE
.LP
The names of these clients are not in the ether channel or local domain
tables because no mail is ever delivered to them - no user has an alias
pointing to any such machine and, of course, the
.I 'multihost'
option ensures that mail sent from these machines contain the site domain name
in the from address.
.LP
The same configuration runs on the NFS servers which can deliver mail locally;
on these servers the sendmail daemon is started with
.DS
/usr/lib/sendmail -q1h -bd
.DE
.LP
in the usual way.
.NH
The configuration 'gateway'
.LP
The host
.I gateway
has access to the ethernet and also has access to JANET, the X.25 based
UK academic network.
This configuration uses a number of domain tables derived from the NRS
(Name Registration Scheme) database. These are produced automatically
by the
.I c-nrs
program (provided with unix-niftp package). For example, the
.I "uk.dom"
domain table maps institution names to full domain names, with entries
like:
.DS
glasgow    glasgow.ac.uk
.DE
.LP
Many sites in the NRS have an abbreviated (or short) name and
standard (or long) name, which are different. For example, the
short form for
.I cs.glasgow.ac.uk
is
.I cs.gla.ac.uk .
Some sites like to rewrite one form into the other (e.g. convert all
addresses into standard form) and c-nrs provides
a table in which to do this. However, with 300+ entries, this is
probably only advisable with IDA sendmail where the table can be
compiled to an IDA database.
.LP
Similarly, there are essentially two ways to set up the janet channel table
depending on how much you want sendmail to do, and how much you leave
to the FTP system to do:
.IP (a)
use just wildcards to effectively pass all (unmatched)
uk.ac and uk.co addresses to the FTP system for "routing".
The unix-niftp system has its own NRS database (using dbm lookup).
Local overrides, for example, known uk.co sites which are not NRS
registered could be placed in the FTP tables or the janet channel table.
.IP (b)
Put all entries into the janet channel (with no wildcards).
This has the advantages that verification of addresses is done by
sendmail directly and that where application relays are involved
the JNT header includes the relay domain (minor point).
However, addresses should be mapped to
a single form in the domain tables so that only one entry is needed
per host in the channel table.  Again, this approach is probably only
advisable with IDA sendmail where both the domain and channel tables
can be compiled to ida databases, otherwise your sendmail may run
rather slowly.
.NH 2
The configuration description 'config.gateway'
.DS I
#basic settings
config=gateway
domain="cs.glasgow.ac.uk"
options=multihost,nrsformat
postmaster=mailer-daemon
install=-f
tabledir=tables

# domain tables
domain std file="cs-dept.ether.chn"
domain std file="glasgow.uk.dom"    # generated by c-nrs
domain std file="glasgow.gla.dom"    # generated by c-nrs
domain std file="glasgow.local.dom"
domain std file="glasgow.ukuucp.dom"
domain top file="glasgow.top.dom"

# channels
channel local file="cs-dept.local.chn",
        showuucp,shownrs,showldomain
channel ether file="cs-dept.ether.chn"
channel ether file="cs-dept.uucp.chn"
channel news file="cs-dept.news.chn",relayed
channel janet file="gateway.janet.chn",auth
channel top file="glasgow.top.dom"
.DE
.LP
There are some notable differences from the 'slave' configuration:
.SH
install=-f
.LP
This configuration can be installed by "make install". The -f flag
prevents a frozen configuration file (sendmail.fc) from being made
when doing this.
.SH
Domain tables
.LP
The domain tables include two NRS derived tables for mapping subdomains
of "ac.uk", "co.uk" and "glasgow.ac.uk" to full domains.
In addition there is a domain table for mapping uucpnames of hosts connected
to glasgow (via uurelay) to their NRS names, and another with names of hosts
within the university but not on our ethernet and not in the NRS either.
.LP
The file
.I glasgow.top.dom
contains a complete list of top level domains that we recognise.
.SH
Channel tables
.LP
The janet channel table we use contains wildcards, with a few entries
for local overrides - we run vanilla BSD4.3 sendmail.
.LP
The janet channel also has the
.I auth
directive to cause the mailer for that channel to be invoked via
.I authorise(8)
allowing restrictions to be placed on users of the channel. See the
.I
User Guide
.R
and the manual page for
.I authorise
in the
.I Manual
directory for more details.
.LP
The top channel table is the same as the top domain table, specifying
relays for the various top level domains; for example, sending all
NIC based domains like
.I "edu"
and
.I "com"
to
.I nss.cs.ucl.ac.uk .
.LP
Although there is an entry for
.I "uk"
in this table, it is never used because of the wildcards that match all
possible uk addresses in the janet channel table.
If we used IDA sendmail with a complete database of uk domains in the
janet channel, then we need a separate top channel table with no entry
for
.I uk -
this avoids relaying invalid addresses elsewhere.
.NH 2
The configuration description 'config.uurelay'
.LP
The host
.I uurelay
has the news system and is the uucp relay.
It also has all the domain tables as well, as it's a MIPS/1000 and has lots
more spare CPU cycles than 'gateway'.
.DS I
# basic settings
config=uurelay
domain="cs.glasgow.ac.uk"
options=multihost,nrsformat
postmaster=mailer-daemon
install=-f
tabledir=tables

# domain tables
domain std file="cs-dept.ether.chn"
domain std file="glasgow.uk.dom"    # generated by c-nrs
domain std file="glasgow.gla.dom"    # generated by c-nrs
domain std file="glasgow.local.dom"
domain std file="glasgow.ukuucp.dom"
domain top file="glasgow.top.dom"

# channels
channel local file="cs-dept.local.chn",
        shownrs,showuucp,showldomain
channel uucp file="uurelay.uucp.chn",
        ldomain="glasgow.uucp",
        sysname="glasgow",muucp
channel ether file="cs-dept.ether.chn"
channel news file="uurelay.news.chn"
channel top file="uurelay.top.chn"
.DE
.LP
This description shows the use of the uucp channel.
Messages sent by UUCP will have the
local domain name faked as "glasgow.uucp" instead of "cs.glasgow.ac.uk";
the UUCP system name is 'glasgow'; the UUCP mailer is
.I muucp
instead of
.I uux(1) .
.LP
The news channel uses a file specific to this host, because on this host
messages for the news are to be delivered rather than forwarded.