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Mi, 5. Februar 2003, 00:00

POP3 before SMTP mit tpop3d und exim4

Installation und Konfiguration von Exim

Exim ist ein extrem flexibler SMTP-Daemon, entsprechend komplex kann auch die Konfiguration sein. Die Quellen und Dokumentation finden sich auf www.exim.org bzw. einem der vielen Mirrors. In diesem Howto wird Exim in der Version 4.05 verwendet. Leider verwendet Exim immer noch kein Automake, daher muss nach Entpacken der Sourcen ein Verzeichnis namens Local und darin die Datei Makefile erstellt werden. Dazu wird die Datei src/EDITME nach Local/Makefile kopiert. Wegen der Länge dieser Datei wird sie hier nicht komplett abgedruckt, sondern nur die entsprechenden Änderungen, ausgehend vom Standard-Makefile.

EXIM_USER=mail
SUPPORT_MAILDIR=yes
LOOKUP_MYSQL=yes
LOOKUP_INCLUDE=-I <Pfad zu den MySQL-Includes>
LOOKUP_LIBS=-L/usr/local/lib -L/usr/lib \
 -L<Pfad zu den MySQL-Libraries> -lmysqlclient

Mit make und make install wird Exim installiert. Dabei erzeugt Exim auch seine Konfigurationsdatei /etc/exim/configure, an der noch einige Änderungen vorzunehmen sind.

Listing: Exim-Konfiguration

######################################################################
# Runtime configuration file for Exim #
######################################################################
# This is a default configuration file which will operate correctly in
# uncomplicated installations. Please see the manual for a complete list
# of all the runtime configuration options that can be included in a
# configuration file. There are many more than are mentioned here. The
# manual is in the file doc/spec.txt in the Exim distribution as a plain
# ASCII file. Other formats (PostScript, Texinfo, HTML, PDF) are available
# from the Exim ftp sites. The manual is also online at the Exim web sites.
# This file is divided into several parts, all but the first of which are
# headed by a line starting with the word "begin". Only those parts that
# are required need to be present. Blank lines, and lines starting with #
# are ignored.
########### IMPORTANT ########## IMPORTANT ########### IMPORTANT ###########
# #
# Whenever you change Exim's configuration file, you *must* remember to #
# HUP the Exim daemon, because it will not pick up the new configuration #
# until you do. However, any other Exim processes that are started, for #
# example, a process started by an MUA in order to send a message, will #
# see the new configuration as soon as it is in place. #
# #
# You do not need to HUP the daemon for changes in auxiliary files that #
# are referenced from this file. They are read every time they are used. #
# #
# It is usually a good idea to test a new configuration for syntactic #
# correctness before installing it (for example, by running the command #
# "exim -C /config/file.new -bV"). #
# #
########### IMPORTANT ########## IMPORTANT ########### IMPORTANT ###########
######################################################################
# MAIN CONFIGURATION SETTINGS #
######################################################################
# hide verhindert überschreiben von Einstellungen per Kommandozeile durch
nichtberechtigte user
# host/dbname/user/passwd
hide mysql_servers = localhost/virtualemail/email/emailpasswort
# Specify your host's canonical name here. This should normally be the fully
# qualified "official" name of your host. If this option is not set, the
# uname() function is called to obtain the name. In many cases this does
# the right thing and you need not set anything explicitly.
primary_hostname = mail.mailserver.de
# The next three settings create two lists of domains and one list of hosts.
# These lists are referred to later in this configuration using the syntax
# +local_domains, +relay_to_domains, and +relay_from_hosts, respectively. They
# are all colon-separated lists:
domainlist local_domains =
 mysql;select domain_name from domain where domain_name = '$domain'
domainlist relay_to_domains =
 mysql;select login_ip from popbox where
login_ip='$sender_host_address'
hostlist relay_from_hosts = 127.0.0.1:192.168.0.0/24
# Most straightforward access control requirements can be obtained by
# appropriate settings of the above options. In more complicated situations, you
# may need to modify the Access Control List (ACL) which appears later in this
# file.
# The first setting specifies your local domains, for example:
#
# domainlist local_domains = my.first.domain : my.second.domain
#
# You can use "@" to mean "the name of the local host", as in the default
# setting above. This is the name that is specified by primary_hostname,
# as specified above (or defaulted). If you do not want to do any local
# deliveries, remove the "@" from the setting above. If you want to accept mail
# addressed to your host's literal IP address, for example, mail addressed to
# "user@[192.168.23.44]", you can add "@[]" as an item in the local domains
# list. You also need to uncomment "allow_domain_literals" below. This is not
# recommended for today's Internet.
# The second setting specifies domains for which your host is an incoming relay.
# If you are not doing any relaying, you should leave the list empty. However,
# if your host is an MX backup or gateway of some kind for some domains, you
# must set relay_to_domains to match those domains. For example:
#
# domainlist relay_to_domains = *.myco.com : my.friend.org
#
# This will allow any host to relay through your host to those domains.
# See the section of the manual entitled "Control of relaying" for more
# information.
# The third setting specifies hosts that can use your host as an outgoing relay
# to any other host on the Internet. Such a setting commonly refers to a
# complete local network as well as the localhost. For example:
#
# hostlist relay_from_hosts = 127.0.0.1 : 192.168.0.0/16
#
# The "/16" is a bit mask (CIDR notation), not a number of hosts. Note that you
# have to include 127.0.0.1 if you want to allow processes on your host to send
# SMTP mail by using the loopback address. A number of MUAs use this method of
# sending mail.
# All three of these lists may contain many different kinds of item, including
# wildcarded names, regular expressions, and file lookups. See the reference
# manual for details. The lists above are used in the access control list for
# incoming messages. The name of this ACL is defined here:
acl_smtp_rcpt = acl_check_rcpt
# You should not change that setting until you understand how ACLs work.
# Specify the domain you want to be added to all unqualified addresses
# here. An unqualified address is one that does not contain an "@" character
# followed by a domain. For example, "caesar@rome.example" is a fully qualified
# address, but the string "caesar" (i.e. just a login name) is an unqualified
# email address. Unqualified addresses are accepted only from local callers by
# default. See the recipient_unqualified_hosts option if you want to permit
# unqualified addresses from remote sources. If this option is not set, the
# primary_hostname value is used for qualification.
# qualify_domain =
# If you want unqualified recipient addresses to be qualified with a different
# domain to unqualified sender addresses, specify the recipient domain here.
# If this option is not set, the qualify_domain value is used.
# qualify_recipient =
# The following line must be uncommented if you want Exim to recognize
# addresses of the form "user@[10.11.12.13]" that is, with a "domain literal"
# (an IP address) instead of a named domain. The RFCs still require this form,
# but it makes little sense to permit mail to be sent to specific hosts by
# their IP address in the modern Internet. This ancient format has been used
# by those seeking to abuse hosts by using them for unwanted relaying. If you
# really do want to support domain literals, uncomment the following line, and
# see also the "domain_literal" router below.
# allow_domain_literals
# No deliveries will ever be run under the uids of these users (a colon-
# separated list). An attempt to do so causes a panic error to be logged, and
# the delivery to be deferred. This is a paranoic safety catch. Note that the
# default setting means you cannot deliver mail addressed to root as if it
# were a normal user. This isn't usually a problem, as most sites have an alias
# for root that redirects such mail to a human administrator.
never_users = root
# The setting below causes Exim to do a reverse DNS lookup on all incoming
# IP calls, in order to get the true host name. If you feel this is too
# expensive, you can specify the networks for which a lookup is done, or
# remove the setting entirely.
host_lookup = *
# The settings below, which are actually the same as the defaults in the
# code, cause Exim to make RFC 1413 (ident) callbacks for all incoming SMTP
# calls. You can limit the hosts to which these calls are made, and/or change
# the timeout that is used. If you set the timeout to zero, all RFC 1413 calls
# are disabled. RFC 1413 calls are cheap and can provide useful information
# for tracing problem messages, but some hosts and firewalls have problems
# with them. This can result in a timeout instead of an immediate refused
# connection, leading to delays on starting up an SMTP session.
rfc1413_hosts = *
rfc1413_query_timeout = 30s
# By default, Exim expects all envelope addresses to be fully qualified, that
# is, they must contain both a local part and a domain. If you want to accept
# unqualified addresses (just a local part) from certain hosts, you can specify
# these hosts by setting one or both of
#
# sender_unqualified_hosts =
# recipient_unqualified_hosts =
#
# to control sender and recipient addresses, respectively. When this is done,
# unqualified addresses are qualified using the settings of qualify_domain
# and/or qualify_recipient (see above).
# If you want Exim to support the "percent hack" for certain domains,
# uncomment the following line and provide a list of domains. The "percent
# hack" is the feature by which mail addressed to x%y@z (where z is one of
# the domains listed) is locally rerouted to x@y and sent on. If z is not one
# of the "percent hack" domains, x%y is treated as an ordinary local part. This
# hack is rarely needed nowadays; you should not enable it unless you are sure
# that you really need it.
#
# percent_hack_domains =
#
# As well as setting this option you will also need to remove the test
# for local parts containing % in the ACL definition below.
# When Exim can neither deliver a message nor return it to sender, it "freezes"
# the delivery error message (aka "bounce message"). There are also other
# circumstances in which messages get frozen. They will stay on the queue for
# ever unless one of the following options is set.
# This option unfreezes frozen bounce messages after two days, tries
# once more to deliver them, and ignores any delivery failures.
ignore_bounce_errors_after = 2d
# This option cancels (removes) frozen messages that are older than a week. ######################################################################
# ACL CONFIGURATION #
# Specifies access control lists for incoming SMTP mail #
######################################################################
begin acl
# This access control list is used for every RCPT command in an incoming
# SMTP message. The tests are run in order until the address is either
# accepted or denied.
acl_check_rcpt:
 # Accept if the source is local SMTP (i.e. not over TCP/IP). We do this by
 # testing for an empty sending host field.
 accept hosts = :
 # Deny if the local part contains @ or % or / or | or !. These are rarely
 # found in genuine local parts, but are often tried by people looking to
 # circumvent relaying restrictions.
 deny local_parts = ^.*[@%!/|]
 # Accept mail to postmaster in any local domain, regardless of the source,
 # and without verifying the sender.
 # accept local_parts = postmaster
 # domains = +local_domains
 # Deny unless the sender address can be verified.
 require verify = sender
#############################################################################
 # There are no checks on DNS "black" lists because the domains that contain
 # these lists are changing all the time. However, here are two examples of
 # how you could get Exim to perform a DNS black list lookup at this point.
 # The first one denies, while the second just warns.
 #
 # deny message = rejected because $sender_host_address is
 # in a black list at $dnslist_domain\n$dnslist_text
 # dnslists = black.list.example
 #
 # warn message = X-Warning: $sender_host_address is in a black list at $dnslist_domain
 # log_message = found in $dnslist_domain
 # dnslists = black.list.example
#############################################################################
 # Accept if the address is in a local domain, but only if the recipient can
 # be verified. Otherwise deny. The "endpass" line is the border between
 # passing on to the next ACL statement (if tests above it fail) or denying
 # access (if tests below it fail).
 accept domains = +local_domains
 endpass
 message = unknown user
 verify = recipient
 # Accept if the address is in a domain for which we are relaying, but again,
 # only if the recipient can be verified.
# accept domains = +relay_to_domains
# endpass
# message = unrouteable address
# verify = recipient
 # If control reaches this point, the domain is neither in +local_domains
 # nor in +relay_to_domains.
 # Accept if the message comes from one of the hosts for which we are an
 # outgoing relay. Recipient verification is omitted here, because in many
 # cases the clients are dumb MUAs that don't cope well with SMTP error
 # responses. If you are actually relaying out from MTAs, you should probably
 # add recipient verification here.
 accept hosts = +relay_from_hosts
 # Accept if the message arrived over an authenticated connection, from
 # any host. Again, these messages are usually from MUAs, so recipient
 # verification is omitted.
 accept authenticated = *
 # Reaching the end of the ACL causes a "deny", but we might as well give
 # an explicit message.
 deny message = relay not permitted
######################################################################
# ROUTERS CONFIGURATION #
# Specifies how addresses are handled #
######################################################################
# THE ORDER IN WHICH THE ROUTERS ARE DEFINED IS IMPORTANT! #
# An address is passed to each router in turn until it is accepted. #
######################################################################
begin routers
# This router routes to remote hosts over SMTP by explicit IP address,
# when an email address is given in "domain literal" form, for example,
# <user@[192.168.35.64]>. The RFCs require this facility. However, it is
# little-known these days, and has been exploited by evil people seeking
# to abuse SMTP relays. Consequently it is commented out in the default
# configuration. If you uncomment this router, you also need to uncomment
# allow_domain_literals above, so that Exim can recognize the syntax of
# domain literal addresses.
# domain_literal:
# driver = ipliteral
# domains = ! +local_domains
# transport = remote_smtp
# This router routes addresses that are not in local domains by doing a DNS
# lookup on the domain name. Any domain that resolves to 0.0.0.0 or to a
# loopback interface address (127.0.0.0/8) is treated as if it had no DNS
# entry. Note that 0.0.0.0 is the same as 0.0.0.0/32, which is commonly treated
# as the local host inside the network stack. It is not 0.0.0.0/0, the default
# route. If the DNS lookup fails, no further routers are tried because of
# the no_more setting, and consequently the address is unrouteable.
dnslookup:
 driver = dnslookup
 domains = ! +local_domains
 transport = remote_smtp
 ignore_target_hosts = 0.0.0.0 : 127.0.0.0/8
 no_more
# The remaining routers handle addresses in the local domain(s).
# This router handles aliasing using a traditional /etc/aliases file.
#
##### NB You must ensure that /etc/aliases exists. It used to be the case
##### NB that every Unix had that file, because it was the Sendmail default.
##### NB These days, there are systems that don't have it. Your aliases
##### NB file should at least contain an alias for "postmaster".
#
# If any of your aliases expand to pipes or files, you will need to set
# up a user and a group for these deliveries to run under. You can do
# this by uncommenting the "user" option below (changing the user name
# as appropriate) and adding a "group" option if necessary. Alternatively, you
# can specify "user" on the transports that are used. Note that the transports
# listed below are the same as are used for .forward files; you might want
# to set up different ones for pipe and file deliveries from aliases.
# system_aliases:
# driver = redirect
# allow_fail
# allow_defer
# data = ${lookup{$local_part}lsearch{/etc/aliases}}
# user = exim
# file_transport = address_file
# pipe_transport = address_pipe
# This router handles forwarding using traditional .forward files in users'
# home directories. If you want it also to allow mail filtering when a forward
# file starts with the string "# Exim filter", uncomment the "allow_filter"
# option.
# The no_verify setting means that this router is skipped when Exim is
# verifying addresses. Similarly, no_expn means that this router is skipped if
# Exim is processing an EXPN command.
# The check_ancestor option means that if the forward file generates an
# address that is an ancestor of the current one, the current one gets
# passed on instead. This covers the case where A is aliased to B and B
# has a .forward file pointing to A.
# The three transports specified at the end are those that are used when
# forwarding generates a direct delivery to a file, or to a pipe, or sets
# up an auto-reply, respectively.
# This router matches local user mailboxes.
virtual_forward:
 driver = redirect
 allow_defer
 allow_fail
 data = ${lookup mysql {
 \ select remote_name from forwarder left join domain_alias
 \ on domain_alias.domain_name = forwarder.domain_name
 \ where local_part = '$local_part' and
 \ (forwarder.domain_name = '$domain' or alias = '$domain')}}
 forbid_file
 forbid_pipe
 retry_use_local_part
virtual_localuser:
 driver = accept
 condition = ${if eq {}{${lookup mysql {
 \ select mbox_name from popbox left join domain_alias
 \ on domain_alias.domain_name = popbox.domain_name
 \ where local_part = '$local_part'
 \ and (popbox.domain_name = '$domain' or alias = '$domain')}}}
 \ {no}{yes}}
 retry_use_local_part
 transport = virtual_local_delivery
virtual_defaultuser:
 driver = redirect
 allow_defer
 allow_fail
 data = ${lookup mysql
 \ {select remote_name from forwarder left join domain_alias
 \ on domain_alias.domain_name = forwarder.domain_name
 \ where local_part = '_default_' and
 \ (forwarder.domain_name = '$domain' or domain_alias.alias =
'$domain')}}
 forbid_file
 forbid_pipe
 retry_use_local_part
######################################################################
# TRANSPORTS CONFIGURATION #
######################################################################
# ORDER DOES NOT MATTER #
# Only one appropriate transport is called for each delivery. #
######################################################################
# A transport is used only when referenced from a router that successfully
# handles an address.
begin transports
# This transport is used for delivering messages over SMTP connections.
remote_smtp:
 driver = smtp
# This transport is used for local delivery to user mailboxes in traditional
# BSD mailbox format. By default it will be run under the uid and gid of the
# local user, and requires the sticky bit to be set on the /var/mail
directory.
# Some systems use the alternative approach of running mail deliveries under a
# particular group instead of using the sticky bit. The commented options
below
# show how this can be done.
virtual_local_delivery:
 driver = appendfile
 delivery_date_add
 directory = ${lookup
 \ mysql{select path from domain left join domain_alias
 \ on domain_alias.domain_name = domain.domain_name
 \ where domain.domain_name = '$domain' or domain_alias.alias =
'$domain'}
 \ {$value}fail}/
 \ ${lookup
 \ mysql{select mbox_name from popbox left join domain_alias
 \ on popbox.domain_name = domain_alias.domain_name
 \ where (popbox.domain_name = '$domain' or domain_alias.alias =
'$domain')
 \ and local_part = '$local_part'}{$value}fail}
 envelope_to_add
 maildir_format
 mode = 0660
 return_path_add
 user =
 \ ${lookup mysql{
 \ select unix_user from domain left join domain_alias
 \ on domain_alias.domain_name = domain.domain_name
 \ where domain.domain_name = '$domain'
 \ or domain_alias.alias = '$domain'}{$value}fail}
local_delivery:
 driver = appendfile
 file = /var/mail/$local_part
 delivery_date_add
 envelope_to_add
 return_path_add
# group = mail
# mode = 0660
# This transport is used for handling pipe deliveries generated by alias or
# .forward files. If the pipe generates any standard output, it is returned
# to the sender of the message as a delivery error. Set return_fail_output
# instead of return_output if you want this to happen only when the pipe fails
# to complete normally. You can set different transports for aliases and
# forwards if you want to - see the references to address_pipe in the routers
# section above.
address_pipe:
 driver = pipe
 return_output
# This transport is used for handling deliveries directly to files that are
# generated by aliasing or forwarding.
address_file:
 driver = appendfile
 delivery_date_add
 envelope_to_add
 return_path_add
# This transport is used for handling autoreplies generated by the filtering
# option of the userforward router.
address_reply:
 driver = autoreply
######################################################################
# RETRY CONFIGURATION #
######################################################################
begin retry
# This single retry rule applies to all domains and all errors. It specifies
# retries every 15 minutes for 2 hours, then increasing retry intervals,
# starting at 1 hour and increasing each time by a factor of 1.5, up to 16
# hours, then retries every 6 hours until 4 days have passed since the first
# failed delivery.
# Domain Error Retries
# ------ ----- -------
* * F,2h,15m; G,16h,1h,1.5; F,4d,6h
######################################################################
# REWRITE CONFIGURATION #
######################################################################
# There are no rewriting specifications in this default configuration file.
begin rewrite
######################################################################
# AUTHENTICATION CONFIGURATION #
######################################################################
# There are no authenticator specifications in this default configuration
file.
begin authenticators
# End of Exim configuration file

Sowohl der Hostname als auch die Zugangsdaten zur MySQL-Datenbank müssen durch die korrekten Werte ersetzt werden. Mit etwas Glück sollte Exim jetzt laufen und die Grundkonfiguration des E-Mail-Servers abgeschlossen sein.

Fortgeschrittene Funktionen

In der Tabelle domains können wie schon gezeigt mehrere Domänen eingetragen werden. Neue Benutzer-Zugänge werden in die Tabelle popbox eingefügt und sind ohne Neustarts des Exim oder Tpop3d sofort einsatzbereit. Weiterleitung von Mail wird durch die Tabelle forwarder eingerichtet, z.B. INSERT INTO forwarder (domain_name,local_part,remote_name) VALUES ('mailserver.de','postmaster','neu@server2.com')

Einrichtung der Clients

Der SMTP- und POP3-Server für die Clients ist unser neu eingerichter Mail-Server. Der Benutzername wird aus dem eigentlichen Benutzernamen, einem Doppelpunkt und der Domäne zusammengesetzt. Abgesehen davon verhält sich unsere Kombination aus Exim und Tpop3d wie jeder andere Mail-Server.

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