By default, we will now listen directly on various ports [breaking]

This allows us to avoid messing around with changes to iptables and generally makes installation easier for everyone.

If you have an instance of postal before this, you will need to do a couple of things to ensure your installation continues to work.

1. You will need to specify a `fast_server.bind_address` in your postal.yml configuration file. This is the IP that you dedicated to the fast server.
2. You will need to allow Ruby to listen on privileged ports (sudo setcap 'cap_net_bind_service=+ep' /usr/bin/ruby2.3).
3. You will need to remove any iptables rules that you may have added previously to accomodate the older way of doing this.

lib/postal/fast_server/server.rb

@@ -6,14 +6,19 @@ module Postal
     class Server
 
       def run
+        if Postal.config.fast_server.bind_address.blank?
+          Postal.logger_for(:fast_server).info "Cannot start fast server because no bind address has been specified"
+          exit 1
+        end
+
         Thread.abort_on_exception = true
         TrackCertificate
         server_sockets = {
           TCPServer.new(Postal.config.fast_server.bind_address, Postal.config.fast_server.ssl_port) => {:ssl => true},
           TCPServer.new(Postal.config.fast_server.bind_address, Postal.config.fast_server.port)     => {:ssl => false},
         }
-        Postal.logger_for(:fast_server).info("Fast server started listening on HTTP  port #{Postal.config.fast_server.port}")
-        Postal.logger_for(:fast_server).info("Fast server started listening on HTTPS port #{Postal.config.fast_server.ssl_port}")
+        Postal.logger_for(:fast_server).info("Fast server started listening on HTTP (#{Postal.config.fast_server.bind_address}:#{Postal.config.fast_server.port})")
+        Postal.logger_for(:fast_server).info("Fast server started listening on HTTPS port (#{Postal.config.fast_server.bind_address}:#{Postal.config.fast_server.ssl_port})")
         loop do
           client = nil
           ios = select(server_sockets.keys, nil, nil, 1)

lib/postal/smtp_server/server.rb

@@ -7,7 +7,6 @@ module Postal
 
       def initialize(options = {})
         @options = options
-        @options[:ports] ||= Postal.config.smtp_server.ports
         @options[:debug] ||= false
         prepare_environment
       end
@@ -49,7 +48,7 @@ module Postal
         if ENV['SERVER_FD']
           @server = TCPServer.for_fd(ENV['SERVER_FD'].to_i)
         else
-          @server = TCPServer.open('::', @options[:ports].first)
+          @server = TCPServer.open('::', Postal.config.smtp_server.port)
         end
         @server.autoclose = false
         @server.close_on_exec = false
@@ -62,7 +61,7 @@ module Postal
           @server.setsockopt(Socket::SOL_TCP, Socket::TCP_KEEPCNT, 5)
         end
         ENV['SERVER_FD'] = @server.to_i.to_s
-        logger.info "Listening"
+        logger.info "Listening on port #{Postal.config.smtp_server.port}"
       end
 
       def unlisten