History of postmax

Version 32

postmax

The ultimate postfix configuration fully tricked out with maximum quality of service

Created by: Anonymous, Last modification: 29 Apr 2008 (14:02 UTC) by spiderr
This installation guide is intended to walk you through completely setting up a postfix smtp mail server with the maximum spam and anti-virus protection available from the open-source community. This technique is similar to that provided Mac OS X Server Mail with IP and DNS protection. It is an amalgamation of several online tutorials available throughout the net and from the software vendors, but all in one neat and tidy place. Our sincere thanks to all who contributed such wonderful software to make this world a better place.

1. Software Install


yum install postfix spamassassin amavisd-new clamav
chkconfig postfix on
chkconfig clamd on
chkconfig freshclam on
chkconfig amavisd on


For RedHat / CentOS, you might need to get the RPM's from DAG

2. Anti-Virus Configuration

Tweak /etc/amavisd.conf with your host information, and uncomment the clamd scanner

['ClamAV-clamd',
  \&ask_daemon, ["CONTSCAN {}\n", "127.0.0.1:3310"],
  qr/\bOK$/, qr/\bFOUND$/,
  qr/^.*?: (?!Infected Archive)(.*) FOUND$/ ],

You might need to change the socket listed with "127.0.0.1:3310" as listed above. SpamAssassin settings are made in this file. Also, make sure $inet_socket_port = 10024; See detailed explanation of amavisd.conf for more information.


<?php
/etc/init.d/clamd start
service amavisd start
service clamd start
# If you are behind a proxy, you need adjust /etc/freshclam.conf
freshclam
service freshclam start
?>


postconf -e 'content_filter = amavis:127.0.0.1:10024'
postconf -e 'receive_override_options = no_address_mappings'

Append these lines to /etc/postfix/master.cf

amavis unix - - - - 2 smtp
        -o smtp_data_done_timeout=1200
        -o smtp_send_xforward_command=yes
        -o disable_dns_lookups=yes
127.0.0.1:10025 inet n - - - - smtpd
        -o content_filter=
        -o local_recipient_maps=
        -o relay_recipient_maps=
        -o smtpd_restriction_classes=
        -o smtpd_client_restrictions=
        -o smtpd_helo_restrictions=
        -o smtpd_sender_restrictions=
        -o smtpd_recipient_restrictions=permit_mynetworks,reject
        -o mynetworks=127.0.0.0/8
        -o strict_rfc821_envelopes=yes
        -o receive_override_options=no_unknown_recipient_checks,no_header_body_checks
        -o smtpd_bind_address=127.0.0.1

Restart postfix

If you run a server for a significant number of users, you will want to run several virus scans at once. Change the 2 in two places: "- - - - 2" as above in master.cf, and "$max_servers = 2;" in amavisd.conf. These numbers should always match.

3. Test Setup

Use telnet to see if the appropriate ports are open:

telnet yourhost.com 25
telnet localhost 3310
telnet localhost 10025
telnet localhost 10024

4. IP Address Spam Prevention

RBLDNSD

This is a local DNS server database that performs local (e.g. FAST) DNS lookups against a list of dynamic and blacklisted IP's. Successful local lookup means it's on the blacklist and will be rejected.

  1. Install the rbldns RPM (available in Fedora Extras, or source)
  2. Edit your named.conf and add:
    
    zone "clients.blocked.rbl" IN {
            type forward;
            forward first;
            forwarders { 127.0.0.1 port 530; };
    };
    zone "hosts.blocked.rbl" IN {
            type forward;
            forward first;
            forwarders { 127.0.0.1 port 530; };
    };
  3. Edit /etc/sysconfig/rbldnsd and add the following lines:
    
    RBLDNSD="dsbl -r/var/lib/rbldnsd -b 127.0.0.1/530 \
    clients.blocked.rbl:ip4set:clients,dynamic \
    hosts.blocked.rbl:dnset:hosts \
    "
  4. Get the latest RBLDNS databases and move database files to /var/lib/rbldnsd
  5. Gentlepeople, start your daemons: "service restart named; service restart rbldnsd;" Test with telnet localhost 53; and telnet locahost 530;
  6. Preform a test lookup:
    
    $dig @localhost 223.61.83.162.clients.blocked.rbl -t txt
    ;; ANSWER SECTION:
    223.61.83.162.clients.blocked.rbl. 2048 IN TXT "DNSBL. 162.83.61.223 is a known spam source. Mail from 162.83.61.223 is NOT accepted on this server!"
  7. Update the following line of your /etc/postfix/main.cf
    
    smtpd_recipient_restrictions = permit_mynetworks,reject_unauth_destination,reject_rbl_client clients.blocked.rbl,reject_rhsbl_client hosts.blocked.rbl,reject_rhsbl_sender hosts.blocked.rbl

En-masse IP Block Here is a tutorial for Blocking E-mail from China and Korea using Postfix and the Okean CIDR Blocks

5. DNS Spam Prevention

There are two main options DomainKeys, and SenderID.
DomainKeys were invented by Yahoo, SenderID was invented by Microsoft. These are arguably competing techniques, however, implementing both seems to have no ill-effect. Given SenderID was invented by Microsoft, you can be assured Outlook Server SMTP gateways employ SenderID, and are unlikely to support DomainKeys any time soon. In early 2005 when these proposals came out simultaneously, they were seen as competing techniques. As time has passed, they are now seen as more complementary, and typically both are implemented.

DomainKeys

DomainKeys Identified Mail is the newest open-standard e-mail authentication specification. To use DomainKeys, typically a filter or "plugin" is needed for your SMTP gateway. There is a postfix filter that is fairly easy to install and configure. Several perl modules need to be installed:
  1. Install necessary perl modules (make sure you have openssl-devel installed):
    
    cpan -i Crypt::OpenSSL::RSA Mail::Address MIME::Base64 Net::DNS Net::Server Test::More Mail::DKIM Error
  2. download source, extract tarball, cd into directory, and compile source with ./configure --prefix=/usr/local/dkimproxy ; make install
  3. For outbound mail signing, you will need a public/private key combo.
    
    openssl genrsa -out private_domainkey.key 1024
    openssl rsa -in private.key -pubout -out public_domainkey.key
  4. Tweak sample-dkim-init-script.sh and copy to /etc/init.d/dkim - Either make a dkimproxy user or change DKIMPROXYUSER and DKIMPROXYGROUP to postfix. The following are line changes made, adjust to your liking...
    
    *snip*
    DKIMPROXYUSER=postfix
    DKIMPROXYGROUP=postfix
    *snip*
    DKIMPROXY_IN_CFG="/etc/dkimproxy_in.conf"
    DKIMPROXY_OUT_CFG="/etc/dkimproxy_out.conf"
  5. Customize the default in confiugration cp /usr/local/dkimproxy/etc/dkimproxy_in.conf.example /etc/dkimproxy_in.conf and modify /etc/dkimproxy_in.conf
    
    # specify what address/port DKIMproxy should listen on
    listen    127.0.0.1:10026

    # specify what address/port DKIMproxy forwards mail to
    relay     127.0.0.1:10027
  6. Customize the default out confiugration cp /usr/local/dkimproxy/etc/dkimproxy_out.conf.example /etc/dkimproxy_out.conf and modify /etc/dkimproxy_out.conf
    
    # specify what address/port DKIMproxy should listen on
    listen    127.0.0.1:10028

    # specify what address/port DKIMproxy forwards mail to
    relay     127.0.0.1:10029

    # specify what domains DKIMproxy can sign for (comma-separated, no spaces)
    domain    yourdomain.com

    # specify what signatures to add
    signature dkim(c=relaxed)
    signature domainkeys(c=nofws)

    # specify location of the private key
    keyfile   /etc/pki/domainkeys/private.key

    # specify the selector (i.e. the name of the key record put in DNS)
    selector  selector1
  7. start dkim with service dkim start. Test ports are up and running with telnet localhost 10026 and telnet localhost 10027
  8. Add inbound dkim postfix configuration to /etc/postfix/master.cf
    
    #
    # Before-filter SMTP server. Receive mail from the network and
    # pass it to the content filter on localhost port 10026.
    #
    smtp      inet  n       -       n       -       -       smtpd
        -o smtpd_proxy_filter=127.0.0.1:10026
        -o smtpd_client_connection_count_limit=10
    #
    # After-filter SMTP server. Receive mail from the content filter on
    # localhost port 10027.
    #
    127.0.0.1:10027 inet n  -       n       -        -      smtpd
        -o smtpd_authorized_xforward_hosts=127.0.0.0/8
        -o smtpd_client_restrictions=
        -o smtpd_helo_restrictions=
        -o smtpd_sender_restrictions=
        -o smtpd_recipient_restrictions=permit_mynetworks,reject
        -o smtpd_data_restrictions=
        -o mynetworks=127.0.0.0/8
        -o receive_override_options=no_unknown_recipient_checks
  9. Add outbound filter to sign outgoing messages in postfix configuration /etc/postfix/master.cf
    
    <?php
    #
    # modify the default submission service to specify a DomainKeys content filter
    # and restrict it to local clients and SASL authenticated clients only
    #
    submission  inet  n     -       n       -       -       smtpd
        
    -o smtpd_etrn_restrictions=reject
        
    -o smtpd_sasl_auth_enable=yes
        
    -o content_filter=dksign:[127.0.0.1]:10028
        
    -o receive_override_options=no_address_mappings
        
    -o smtpd_recipient_restrictions=permit_mynetworks,permit_sasl_authenticated,reject
    #
    # specify the location of the DomainKeys signing filter
    #
    dksign    unix  -       -       n       -       10      smtp
        
    -o smtp_send_xforward_command=yes
        
    -o smtp_discard_ehlo_keywords=8bitmime
    #
    # service for accepting messages FROM the DomainKeys signing filter
    #
    127.0.0.1:10029 inet  n  -      n       -       10      smtpd
        
    -o content_filter=
        -
    o receive_override_options=no_unknown_recipient_checks,no_header_body_checks
        
    -o smtpd_helo_restrictions=
        -
    o smtpd_client_restrictions=
        -
    o smtpd_sender_restrictions=
        -
    o smtpd_recipient_restrictions=permit_mynetworks,reject
        
    -o mynetworks=127.0.0.0/8
        
    -o smtpd_authorized_xforward_hosts=127.0.0.0/8
    ?>

SenderID (and SPF)

SenderID merged with a smaller group called Sender Policy Framework (SPF). SPF is a very simple mechanism for specifying which servers are valid for sending your email and is much simpler to implement than DomainKeys. Microsoft holds several patents in relation to the SenderID framework, however it released those patents in the "public domain" this past october. Beyond the typical cynicism of Microsoft's ulterior motives, SPF has a significant amount of technical criticism. Regardless, many major ISP's are using SPF to filter mail, including AOL (and RoadRunner) which has in some reports exclusively implemented SPF to some degree. (Spamassassin reports SOFT_FAIL reports from bogus .rr.com emails.) Spamassassin easily supports SPF with a few simple cpan installs.

The quickest way to get the DNS entries up and running is to follow the wizard.

Troubleshooting

  • Be sure to watch your logs, such as: tail -f /var/log/maillog
  • Config tinkering can lead to one of the services being down..
  • On SLES 10, it seems clamd can take up to 10 minutes to begin accepting connections. Reason currenly unknown. Please chime in if you have any ideas.
  • Check your open ports with netstat -lp and you should see somthing like:
    
    # netstat -lp
    Active Internet connections (only servers)
    Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
    tcp        0      0 localhost:10024         *:*                     LISTEN      2011/amavisd (maste
    tcp        0      0 localhost:10025         *:*                     LISTEN      16463/master
    tcp        0      0 localhost:10026         *:*                     LISTEN      15545/perl
    tcp        0      0 *:submission            *:*                     LISTEN      16463/master
    tcp        0      0 localhost:10027         *:*                     LISTEN      16463/master
    tcp        0      0 localhost:10028         *:*                     LISTEN      15554/perl
    tcp        0      0 localhost:10029         *:*                     LISTEN      16463/master
    tcp        0      0 localhost:dyna-access   *:*                     LISTEN      1803/clamd
    tcp        0      0 localhost:domain        *:*                     LISTEN      1875/named
    tcp        0      0 *:smtp                  *:*                     LISTEN      16463/master

References and Other tutorails

http://devnull.com/kyler/dspam.20040512.html
http://howtoforge.com/virtual-users-domains-postfix-courier-mysql-squirrelmail-mandriva2008.1-p3
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