NAME
couriermlm - The Courier mailing list manager
SYNOPSIS
couriermlm {command} {directory} [arg...]
DESCRIPTION
couriermlm is the Courier mail server´s mailing list manager. This
command sets up, maintains, and manages mailing lists. couriermlm
automatically handles requests to subscribe and unsubscribe list
members, detects undeliverable addresses and removes them from the
subscription rolls. Mailing lists managed by couriermlm require zero
human administrative oversight. couriermlm supports digests,
write-only posting aliases, and moderated mailing lists.
CREATING A MAILING LIST
Anyone can use couriermlm, not just the system administrator. The
Courier mail server mail server translates an address list-name@domain
as a local address with a corresponding dot-courier(5)[1] file. Anyone
that can install a dot-courier(5)[1] file, and can schedule cron(8)
jobs, can run a couriermlm mailing list.
Note that the system administrator can optionally remove the dot-
courier(5)[1] support from the the Courier mail server. couriermlm
will not work in that case.
Setting up a mailing list consists of the following steps:
Run couriermlm create
Use this command to create a directory where couriermlm keeps all
mailing list related files.
Configure the mailing list
The couriermlm create command initializes the mailing list
subdirectory with some default template responses. It is necessary
to customize them for your mailing list, and it may be necessary to
issue some additional commands in order to configure appropriate
mailing list options -- such as enabling unrestricted posting
privileges, and enabling moderation.
Create dot-courier(5)[1] files
Set up to run couriermlm to distribute mailing list messages, and
process requests.
Set up cron(8)
You need to set up cron(8) jobs to run the couriermlm hourly and
couriermlm daily commands, which perform regular mailing list
maintenance.
Back up subscription lists
As part of your daily job you should also run the export command,
in order to back up the mailing list subscriber information. In the
event that the mailing list database gets corrupted or lost, you
can restore it from this backup file. See the export command for
more information.
Note
Setting up a digest for the mailing list requires additional steps.
See "Setting up a mailing list digest[2]" below for more
information.
The first step is to run the following command:
couriermlm create directory ADDRESS=list@domain
directory is the mailing list directory that will be managed by
couriermlm. This directory should not be created in advance, this
command creates this directory, and initializes it.
list@domain is the mailing list´s address, the address that sends
messages to the mailing list.
An additional setting, URL may also be specified:
couriermlm create directory ADDRESS=list@domain URL=url
“url” would be the URL of the WebMLM web page for this mailing list.
See webmlmd(1)[3] for more information.
The directory created by couriermlm create is initialized to contain a
number of text files that couriermlm sends back as replies to
administrative commands. It is necessary to edit these template files
and adjust the text in those files for this mailing list. All template
filenames end with .tmpl, and their contents are self explanatory. Some
important template files are:
help.tmpl
This text is returned in response to the help command. This text
must be modified depending upon whether this mailing list is a
moderated mailing list, has a digest version, or if any other
non-default configuration options are set for the mailing list.
sub.tmpl
This is the reply that´s sent back in response to a subscription
request. Less important is unsub.tmpl, which is the response to a
request to unsubscribe.
sub2.tmpl
This is the successful subscription confirmation. A brief overview
of the mailing list might be appropriate here.
couriermlm has rudimentary support for non-English templates. The
couriermlm create command has a single, optional parameter,
--lang=suffix The option must be specified after the mailing list
directory´s name:
couriermlm create directory --lang=es ADDRESS=list@domain URL=url
The templates for the stock text files come from
/usr/lib/courier/couriermlm. This directory contains all the *.tmpl and
*.html template files that couriermlm create installs in the new
mailing list directory.
Translated versions of template files are installed in the same
directory, /usr/lib/courier/couriermlm. The translated version of file
must be installed as file.suffix, for example: help.tmpl.es is the
translated version of help.tmpl, with the “es” suffix.
The --lang=suffix option installs the the .suffix version of each text
template file, if available. If not, the stock English template file
gets copied, as usual.
Note
Do not remove the English template files, even if you never use
them. They must be left in place, in /usr/lib/courier/couriermlm,
for couriermlm create to work correctly.
Example:
couriermlm create /home/lists/users-list --lang=es ...
This example installs the *.es versions of mailing list template files.
Only the stock, English template files come with the Courier mail
server. This mechanism only provides an easy integration ability with
template files from other sources.
There are some additional configuration files that can be modified to
suit your taste:
headeradd
This file can be initialized to contain any mail headers that will
be automatically added to every mailing list message. The contents
of this file are simply prepended to every message that goes out.
Blank lines are not allowed.
headerdel
This file lists any headers that will be automatically removed from
every mailing list message before it´s sent. List each header one
per line, including the : character. For example, to remove all
Received: and Date: headers from every message, initialize this
file to contain the following two lines:
Received:
Date:
Both the headeradd and headerdel files can be used to implement a
popular feature of setting the replies to every message to go to the
mailing list. Having "Reply-To:" in headerdel, removes any existing
Reply-To: header, and then having "Reply-To: list@domain" in headeradd
appends a fixed Reply-To: header to every message.
The create command also creates the following subdirectories in the
mailing list directory:
sublist
This subdirectory has the database files that contain the mailing
list´s subscription list.
unsublist
This subdirectory stores files that contain information about
addresses that have been unsubscribed from the mailing list. This
information might be of some use when tracking down an old
subscription. The contents of this directory are not automatically
purged, you must set up your own purging mechanism for this
directory.
commands, commands.dat
These directories store temporary files that contain pending
(unconfirmed) commands for the mailing list manager. The couriermlm
commands hourly and daily must be executed regularly in order to
periodically purge stale entries.
modqueue
Messages awaiting moderator approval (for moderated lists).
archive
Messages received by this mailing list will be stored here, in
addition to being forwarded to subscribers. couriermlm does not
automatically do any purging on this subdirectory, you must set up
your own archiving mechanism that cleans out this subdirectory.
The last step involves installing a couple of dot-courier(5)[1] files
that run couriermlm to receive mailing list messages and administrative
commands. The mailing list address, list@domain, corresponds to some
dot-courier(5)[1] file. For example, if your system account is john,
and your mail domain is example.com, then the dot-courier(5)[1] file
for the mailing list <john-list@example.com> is $HOME/.courier-list.
Let´s say that the dot-courier(5)[1] file is $HOME/.courier-list. To
properly support the mailing list, the following dot-courier(5)[1]
files will have to be initialized as follows:
$HOME/.courier-list
This file should be initialized to contain the following delivery
instruction:
| /usr/bin/couriermlm msg directory
directory is the created mailing list directory.
$HOME/.courier-list-owner
This file should contain the appropriate delivery instructions for
forwarding all mail addressed to <list-owner@domain> to the address
of the owner of the mailing list. This can be another E-mail
address, or a mailbox specification.
$HOME/.courier-list-default
This file should be initialized to contain the following delivery
instruction:
| /usr/bin/couriermlm ctlmsg directory
directory is the created mailing list directory. This dot-
courier(5)[1] file provides support for all other addresses of the
form <list-command@domain>, where command is a mailing list
administrative command. Commands are sent to this mailing list
manager by sending a message to one of several special addresses,
described more fully in "Mailing list commands[4]", below.
MANUAL COMMANDS
couriermlm may also be run manually from the command line as follows:
/usr/bin/couriermlm command directory [ options... ]
command is a command from the following list. directory is the mailing
list directory. The commands are:
create
Create a mailing list.
update
Update/restore mailing list templates. The original, default,
mailing list message template files (*.tmpl and *.tmpl.html) are
reinstalled into the mailing list directory. This command must be
processed for every mailing list directory after upgrading to the
Courier server version 0.55, or later, from earlier versions (but
see below). couriermlm in version 0.55 of the Courier mail server
uses updated templates files, which must be installed in every
mailing list directory. Although the names of many template files
have not changed, the embedded markup codes in the template files
work differently.
1. Begin by making a backup copy of all *.tmpl files in the
existing couriermlm mailing list directory.
2. Run the “update” command on the list directory.
3. Review the backed up template files, identify your customized
changes, then retype them into new template files installed by
the “update” command.
4. Proceed to the next mailing list directory.
Yes, this is going to be a pain. This is the first overhaul of
couriermlm´s infrastructure in many years. Once a decade, some
elbow grease must be sacrificed in the name of progress. It´s
not the end of the world.
In an extreme emergency, preserve the couriermlm from the
previous version of the Courier mail server. Mass-update all
existing lists´ .courier-list and .courier-list-default files
to run the old couriermlm. Then, migrate each mailing list on a
predetermined schedule. After migrating each list, put the
default path back into the list´s .courier files.
Keep in mind the following issues, while migrating the lists:
· The help.tmpl template file is usually the one that gets
customized the most. In most cases, large bits and pieces
of this file, that document certain list options that do
not apply to this list, must be removed.
· There are several new template files, including a number of
*.html files that refer to new HTML-formatted responses
from couriermlm, and the WebMLM interface.
· Be aware of updated mail headers declared in several
template files. The MIME character set is now given as
utf-8. Some templates no longer contain the Mime-Version
and Subject headers. The Subject headers are moved to
separate template files. Many existing template files now
contain both a plain text and an HTML-formatted version of
the couriermlm response. Always scroll to the end of each
template file, to reveal any appended HTML portion of
template´s text.
set
Set mailing list options.
sub
Manually subscribe an address to the mailing list.
unsub
Manually unsubscribe an address from the mailing list.
lsub
List all the subscribers to this mailing list.
laliases
List write-only aliases for this mailing list.
export
Export mailing list subscriber information.
import
Import mailing list subscriber information.
ctlmsg
Receive and interpret a control message.
info
Display a subscription record.
msg
Post a message to the mailing list.
hourly
Perform hourly maintenance. It is necessary to set up a cron(8)
job to execute the hourly command once an hour.
daily
Perform daily maintenance. It is necessary to set up a cron(8)
job to execute the daily command once a day.
digest
Create a digest. See "Setting up a mailing list digest[2]"
below for more information.
MANUAL SUBSCRIPTION MANAGEMENT
The sub, unsub, lsub, laliases, export, and import commands allow
manual subscription list management. Normally, subscription-related
commands are done by sending an appropriate mailing list command, see
"Mailing List Commands[4]", below.
couriermlm sub directory user@domain
This command adds the address <user@domain> to the subscription list.
couriermlm will now read a free-form comment or a note from standard
input, terminated by an end-of-file (usually CTRL-D). The free-form
comment is stored in the subscription database, together with the
address, and is shown by the "info" command.
couriermlm unsub directory user@domain
This command remove the address <user@domain> from the subscription
rolls. couriermlm will also read a free-form comment, which is added
to the subscription record. After removing this address from the
subscription rolls, its subscription record is archived in the
directory/unsublist directory.
couriermlm lsub directory
This command lists all the addresses subscribed to the list, on
standard output, one per line.
couriermlm laliases directory
This command lists all write-only aliases that have been subscribed to
the list, together with the subscriber address that added each alias.
See "Write-Only Aliases[5]" for more information.
couriermlm export directory
The export command lists the contents of the subscription database on
standard output. The export command produces the following output
format:
address
subscription information
...
address
subscription information
...
"address", is an address subscribed to the mailing list. This is
followed by its corresponding subscription information, usually a copy
of the subscription request that was used to add the address to the
mailing list. The subscription information is terminated by a line
containing a single period. Any lines in the subscription information
that begin with a period have an extra period prepended to them.
couriermlm import directory
The import command reads on standard input a previously exported
mailing list subscription database, and adds those addresses to the
indicated mailing list.
It is highly recommended to make a regular backup of subscriber
information using the export command, in the event that the
subscription database gets corrupted. In which case the import command
can be used to rebuild the subscription database, in absence of any
direct backups of the database files.
SETTING MAILING LIST OPTIONS
The set command sets various list options:
couriermlm set directory option=value option=value...
Note
Setting the ADDRESS or the URL options, described below,
automatically updates the contents of the headeradd configuration
file. Its existing “List-” headers are removed and replaced by
updated “List-” headers that reflect the revised list address or
URL.
One or more options can be set with the same command. The available
options are:
ADDRESS=address
The base E-mail address for this mailing list.
URL=address
The URL of WebMLM web page for this mailing list.
Note
WebMLM determines its own URL automatically, by reading its
HTTP headers. This setting is used by couriermlm, which has no
knowledge of the web server´s configuration, and needs to know
the correct URL to insert into generated messages.
CASESENSITIVE=flag
If flag is "1", the userid portion of E-mail addresses are
case-sensitive. The domain address portion is always
case-insensitive. The default setting is "0" making both userid and
domain address portions of E-mail addresses case-insensitive.
Note
Be careful when changing this setting on an active list.
Changing this option to “CASESENSITIVE=1”, forces all existing
subscribers to make sure their addresses are lowercase-only,
otherwise they will no longer be recognized as subscribers.
Changing this option to “CASESENSITIVE=0” blocks all subscribed
addresses that have uppercase characters in the userid portion
of their E-mail address. They will continue to receive mailing
list traffic, but unable to post messages to the list, or
unsubscribe from it. It will not be possible to unsubscribe
those addresses even by running the couriermlm command
manually.
DIGEST=directory
Enable digests. directory is the pathname to the
previously-createddigest list directory. See "Setting up a mailing
list digest[2]" below for more information.
KEYWORD=keyword
Set the subject line keyword for mailing list messages. If set,
couriermlm inserts "[keyword]" into the subject of every mailing
list message, to aid sorting by the recipients.
MAXBOUNCES=n
Maximum number of bounce notifications sent by the hourly command,
in order to prevent the mail system from being overloaded. The
default is 20 bounce notifications. Any unsent notifications will
be carried over to the next hourly job.
MAXMODNOTICES=n
Maximum number of moderation reminders sent by the hourly command,
in order to prevent the mail system from being overloaded. The
default is 20 moderation reminders. Any unsent reminders will be
carried over to the next hourly job.
MAXFETCHSIZE=K
Maximum size, in kilobytes, of a response to the fetch command. The
default is 100Kb. This option is used to minimize the impact of
abusive requests for the entire archive, with a forged return
address.
NAME=name
The name that´s listed on the return address of administrative
messages. Note that if name contains spaces, you should quote this
argument in the shell. The default value is "Courier Mailing List
Manager".
NOBOZOS=flag
If flag is "0" couriermlm will not attempt to block misdirected
subscribes and unsubscribes that are sent to the mailing list´s
posting address. If flag is "1" (the default), those kinds of
messages will be bounced appropriately.
NODSN=flag
If flag is "1" couriermlm will use a Delivery Status Notification
setting of "never" when it sends confirmation requests and help
messages: this should reduce the amount of useless failure
notifications generated when couriermlm dutifully replies to spam
received by the mailing list administrative addresses, i.e.
-(un)subscribe and -help. If flag is "0" (the default), a DSN
setting of "fail" will be used. Please see sendmail(1)´s -n option
for more details on the DSN setting.
POST=option
Set posting options. option is one of three values: "subscribers"
- only subscribers may post messages to this mailing list (this is
the default); "all" - anyone can post messages to this mailing
list; "mod" - only subscribers may post, and messages are sent to
the list owner for approval (moderation).
POSTARCHIVE=option
Set access to archived messages. option is either: "all" - Anyone
can access the mailing list archive; or "subscribers" - only
subscribers can access the archive. The default is "all".
PURGEARCHIVE=d
Purge archived mailing list messages after d days. The default is 0
days - messages are never removed from the archive subdirectory.
PURGEBOUNCE=d
Wait d days for the probe message, that automatically unsubscribes
undeliverable addresses, to bounce (default: 14 days). Probe
messages are sent three days (default) after the first message to
an address bounces.
PURGECMD=h
Purge unconfirmed subscribe/unsubscribe requests after h hours
(default: 48 hours).
REMODERATE=h
Resend a moderation reminder after h hours (default: 12 hours).
REPORTADDR=address
Mail daily reports of new and removed subscribers to this address.
Must be set in order to receive reports. Provide an empty address
to stop reporting.
SIMPLECONFIRM=n
If n is 1, confirmation requests may be acknowledged without adding
“yes” to the subject line.
Note
The text in sub.tmpl, unsub.tmpl, and help.tmpl may need
adjusting.
SUBSCRIBE=option
Set subscription options. option is either "all", meaning that
anyone can subscribe, or "mod", meaning moderated subscription
requests, where all subscription requests are sent to the mailing
list owner for approval. The default is "all".
STARTPROBE=n
Send a probe to a bouncing address n days after receiving the first
bounce. Basically this means that an address must bounce for at
least n days before it gets a probe message. The default is 3 days.
Option names and settings are case sensitive.
Note
If you set up a digest list, you MUST set identical POSTARCHIVE
option for both the main list and the digest list.
DISPLAYING A SUBSCRIPTION RECORD
The info command displays the subscription record for the requested
address:
couriermlm info directory user@domain
This displays the subscription record for "user@domain", which
typically consists of a copy of the initial subscription request, and
confirmation.
SENDING MESSAGES TO THE MAILING LIST
The msg commands reads an E-mail message on standard input, and mails
the contents of the message to the mailing list´s subscribers.
If the POST option is set to "subscribers", the message is rejected
unless the address in its From: header is a subscriber to this mailing
list.
Control files headeradd and headerdel are read, and are applied to the
message, as described previously.
MAILING LIST COMMANDS
Mailing list commands can be sent via E-mail to couriermlm by sending a
message to <list-command@domain>. The "default" dot-courier(5)[1] file
runs couriermlm to receive mail for all addresses of this form.
couriermlm reads the DEFAULT environment variable, which is set by the
Courier mail server, that indicates the specific command. The available
commands are:
help
A simple autoresponder. couriermlm mails the sender the contents
of the help.tmpl file.
subscribe
A request to subscribe to this mailing list. couriermlm reads the
sender´s address in order to determine what address to subscribe.
subscribe-name=domain
Explicitly specify the address to subscribe to the mailing list,
instead of using a return address. In the previous example, sending
a message addressed to
<my-widgets-subscribe-john=domain.com@example.com> would result in
a subscription request for <john=domain.com>. Any unusual
punctuation characters in the address must be replaced by a plus
sign, followed by two hexadecimal digits that represent the
punctuation character´s ASCII code.
unsubscribe
A request to unsubscribe to this mailing list.
unsubscribe-name=domain
Explicitly specify the address to unsubscribe from the mailing
list.
alias-subscribe
Set up a write-only alias (see below).
alias-subscribe-name=domain
Explicitly specify the subscriber address for which a write-only
alias needs to be set up.
There are other commands that are used internally for maintaining the
mailing list.
WRITE-ONLY ALIASES
Write-only E-mail aliases can send messages to the mailing list, but
they do not receive any mailing list messages themselves. A write-only
alias can be set up by any subscriber. Only one write-only alias is
allowed per subscribed E-mail address. Write-only aliases are not
needed for mailing list that has the POST=all option set.
To set up a write-only alias, the subscriber sends a couriermlm
alias-subscribe command. The subscriber´s E-mail address can be
explicitly specified in a similar manner as the subscribe command.
The subject line of the E-mail message must contain the E-mail
write-only alias to be set up, and nothing else. couriermlm responds
with a confirmation request, just like when subscribing to the list.
This request must be acknowledged in the same way.
A subscriber´s write-only alias can be changed at any time by repeating
this procedure. The new alias replaces the previous one. To prevent
abuse, there´s a limit of at most one alias-subscribe command every 30
minutes.
Leave the subject of the E-mail message blank in order to remove an
existing write-only alias,
SETTING UP A MAILING LIST DIGEST
couriermlm supports mailing list digests. Mailing list digests are
created as a second, separate, mailing list. The create command
initializes a second mailing list directory, and then additional
configuration takes place which links the main mailing list to the
digest list.
If the mailing list address is list-address@example.com, the address of
the digest version of the mailing list is usually
list-address-digest@example.com, but it doesn´t have to be this
address. The only requirement is that the directory for the digest
version of the mailing list must reside on the same file system as the
directory for the mailing list itself, and both must be owned by the
same userid.
To set up a mailing list digest, first proceed with the steps to create
the mailing list itself. After the mailing list is created and
configured, proceed as follows:
Create the digest list directory
Execute the create command to create the digest version of the
list:
/usr/bin/couriermlm create \
/path/to/digest/list/directory \
ADDRESS=list-address-digest@example.com
Use the full pathname to the mailing list directory, and the
address of the digest version of the mailing list.
Configure the digest list
Execute the set command to set any appropriate options for the
digest list. There one important differences to note: messages are
not posted to the digest list directly, so there is no moderation
option, however the digest version of the list can have moderated
subscription requests.
Link the two lists
Set the DIGEST option for the main mailing list, specifying the
directory of the digest list. This keyword lets couriermlm know
that a digest version is available.
Note
You MUST set identical POSTARCHIVE option for both the main
list, and the digest list.
Create dot-courier(5)[1] files
It is necessary to create dot-courier(5)[1] files for the digest
list just like the main list, except for some important
differences, which are noted below.
Create cron(8) jobs
It is also necessary to create cron jobs for the digest list
exactly like the main list, to run the hourly and daily cleanup.
It´s possible to set up one set of cron jobs to run hourly and
daily cleanups consecutively for both lists.
Create a digest cron(8) job
The digest creates and distributes the digest version of the list.
It can be executed by a cron(8) job, or the command can be executed
manually.
The main mailing list is supported by three dot-courier(5)[1] files, as
previously described: the posting address, the owner forwarding
address, and the default address that handles administrative control
messages. In the following example, the names $HOME/.courier-list,
$HOME/.courier-list-owner, and $HOME/.courier-list-default are used to
represent each one of these files, and the following names are used to
represent the dot-courier(5)[1] files that correspond to the digest
version of the mailing list: $HOME/.courier-list-digest,
$HOME/.courier-list-digest-owner, and
$HOME/.courier-list-digest-default. Note, however, that the digest
version of the mailing list can have any name, not necessary the name
of the list, followed by "digest".
The contents of both $HOME/.courier-list $HOME/.courier-list-digest
must be the same. Sending a message to the digest address should really
end up sending a message to the main mailing list. Do not put the
address of the digest mailing list directory in
$HOME/.courier-list-digest, instead specify the address of the main
mailing list directory. Just copy $HOME/.courier-list to
$HOME/.courier-list-digest.
However, the contents of $HOME/.courier-list-digest-default must
specify the directory of the digest version of the mailing list. The
digest list is managed separately from the main list, it has its own
subscriber list that is separate from the list of subscribers to the
main list. $HOME/.courier-list-default can simply be copied to
$HOME/.courier-list-digest-default, then the directory can be changed
in the latter.
$HOME/.courier-list-owner may use the same mailing list owner address
as $HOME/.courier-list-digest-owner, or it can specify a different
address. The both the digest and the main mailing list can have the
same mailing list owner/moderator, or have a different owner/moderator.
The following command must be executed in order to link the two lists
together:
/usr/bin/couriermlm set \
/path/to/main/list/directory \
DIGEST=/path/to/digest/list/directory
Setting the DIGEST option on the main list lets couriermlm know that a
digest version is available. The DIGEST option must either use an
absolute pathname, or a pathname that´s relative to the main list
directory (NOT the current directory).
When the DIGEST option is set, messages are simultaneously distributed
to the mailing list´s subscribers, saved in the archive subdirectory of
the main list, then placed in the modqueue subdirectory of the digest
list. Digest list do not employ moderation -- any moderation must take
place on the main list -- so the modqueue subdirectory is recycled to
compile individual messages for the digest.
Finally, something needs to be done in order to actually distribute the
digest to the digest list´s subscribers. This is done by running the
following command:
/usr/bin/couriermlm digest /path/to/digest/directory N H
This command creates a digest, and sends it out. The N and H arguments
are optional. The digest is created only if there´s at least N messages
that are waiting to be sent in the digest list, or if the oldest
message is at least H hours old. Both options default to 0, so the
default behavior is to send a digest with all unsent messages.
Note that when the digest is created, ALL unsent messages are packaged
into the digest, even if some messages are more recent than the time
interval specified by the H option. A cron(8) job can be set up to run
the digest command, or run it manually.
couriermlm automatically provides the From:, To: headers on a message
digest. Additional headers may be specified by the headeradd file in
the digest list directory. The headerdel file has no effect. Note that
the individual messages in the digest are copies of the messages from
the main mailing list, and thus have the headeradd and headerdel
headers processed from the main mailing list directory.
BUGS
couriermlm will not work if the Courier mail server´s support for dot-
courier(5)[1] extensions is disabled.
SEE ALSO
courier(8)[6], dot-courier(5)[1], webmlmd(1)[3].
NOTES
1. dot-courier(5)
[set $man.base.url.for.relative.links]/dot-courier.html
2. Setting up a mailing list digest
[set $man.base.url.for.relative.links]/#digest
3. webmlmd(1)
[set $man.base.url.for.relative.links]/webmlmd.html
4. Mailing list commands
[set $man.base.url.for.relative.links]/#command
5. Write-Only Aliases
[set $man.base.url.for.relative.links]/#wonly
6. courier(8)
[set $man.base.url.for.relative.links]/courier.html