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A port of OpenBSD spamd to Linux iptables

This is a port of the OpenBSD spam deferral daemon spamd to Linux and iptables.

Setup

  1. Make and install

     $ make
 # make install

  2. Install config files

     # mkdir /etc/obspamd
 # echo "@example.com" > /etc/obspamd/alloweddomains
 # cp etc/obspamd.conf.sample /etc/obspamd/obspamd.conf
 # $EDITOR /etc/obspamd/obspamd.conf

  3. Setup cron

    Configure cron to run /usr/local/sbin/obspamd-setup once every few hours to setup any blacklists you've configured in obspamd.conf.

  4. Install required service entries

    obspamd uses getservbyname to find what ports to use:

     # cat etc/services >> /etc/services

  5. Redirect iptables logs to obspamlogd

    Make iptables log all SMTP connections so obspamlogd can update its database:

     # iptables -A INPUT -p tcp -m tcp --dport 25 --tcp-flags FIN,SYN,RST,ACK SYN -j LOG --log-prefix "obspamlogd: "
 # iptables -A OUTPUT -p tcp -m tcp --dport 25 --tcp-flags FIN,SYN,RST,ACK SYN -j LOG --log-prefix "obspamlogd: "

    obspamlogd reads the above iptables kernel logs via a pipe. If you're using rsyslog, there is a sample config file you can use:

     # cp etc/rsyslog.conf /etc/rsyslog.d/obspamlogd.conf

  6. Setup iptables

    Create a chain in the nat table where whitelisted connections are placed:

     # iptables -t nat -N spamd-white

    Setup iptables to redirect incoming connections to obspamd:

     # iptables -t nat -A PREROUTING -p tcp -m tcp --dport 25 -j spamd-white
 # iptables -t nat -A PREROUTING -p tcp -m tcp --dport 25 -j REDIRECT --to-ports 8025
 # iptables -t nat -A spamd-white -j RETURN

    You also need to accept whitelisted connections to port 25 and 8025 (the obspamd port):

     # iptables -A INPUT -p tcp -m tcp --dport 8025 -j ACCEPT
 # iptables -A INPUT -p tcp -m tcp --dport 25 -j ACCEPT

License

OpenBSD spamd uses the ISC and BSD licenses. See each individual file for details.

Build

It was done into a Ubuntu 14.04. It required:

  • GNU make
  • gcc
  • libdb-dev