This is a patch to fetch emails from POP server instead of IMAP (based on IMAP handling code)

Copy attahced pop3.rb into +lib\redmine+ directory

require 'net/pop'

module Redmine
  module POP3
    class << self
      def check(pop_options={}, options={})
        host = pop_options[:host] || '127.0.0.1'
        port = pop_options[:port] || '110'

        pop = Net::POP3.new(host,port)
        pop.start(pop_options[:username], pop_options[:password]) do |pop_session|
          pop_session.each_mail do |msg|
            message = msg.pop
            logger.debug "Receiving message: #{message.grep(/^Subject: /)}" if logger && logger.debug?
            if MailHandler.receive(message, options)
              logger.info "Message #{message.grep(/^Subject: /)} processed -- removing from server." if logger && logger.info?
              puts "#{message.grep(/^Subject: /)}"
              puts "--> Message processed and deleted from the server"
              msg.delete
            else
              puts "#{message.grep(/^Subject: /)}"
              puts "--> Message NOT processed -- leaving it on the server"
              logger.info "ERROR: Message #{message.grep(/^Subject: /)} can not be processed, leaving on the server." if logger && logger.info?
            end

          end
        end
 
      end
      
      private
      
      def logger
        RAILS_DEFAULT_LOGGER
      end
    end
  end
end

and add the new task to email.rake file in lib\tasks

    task :receive_pop => :environment do
      pop_options  = {:host => ENV['host'],
                      :port => ENV['port'],
                      :username => ENV['username'],
                      :password => ENV['password']}
                      
      options = { :issue => {} }
      %w(project status tracker category priority).each { |a| options[:issue][a.to_sym] = ENV[a] if ENV[a] }
      options[:allow_override] = ENV['allow_override'] if ENV['allow_override']

      Redmine::POP3.check(pop_options, options)
    end