Following up on my earlier post where I covered how to backup your Gmail account using "fetchmail" and "procmail"; I wanted to cover how I was additionally processing received mail through ruby.

This was part of a larger project where I was doing statistical analysis on my email while evaluating various data stores. To get the emails into the various data stores, I used the ruby script to parse, process and store the emails as they came in.

If you're going to be doing any form of mail manipulation or statistics I highly recommend the mail gem. It did almost everything I needed out of the box, though it didn't correctly enumerate any of the additional headers.

Procmail is a highly flexible mail filtering and local delivery agent. Without much effort you can pass the mail it is handling through a series of filters which can manipulate and reject mail before eventually delivering it to your inbox. In light of this, we're going to make a filter that simply counts the total number of emails the script has processed, and add a header to the message that indicates this count.

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#!/usr/bin/env ruby

require 'mail'

# Get the email message from STDIN or a passed filename
message = ""
while input = ARGF.gets
  message += input
end

# Parse the email into a ruby object
msg = Mail.new(message)

# Location of our count file
count_file = "#{ENV['HOME']}/.mail_counter.txt"

# Load or initialize our count value and increment it
count = File.exists?(count_file) ? File.read(count_file).to_i : 0
count += 1

# Update our count on disk
File.write(count_file, count.to_s)

# Add our header with the count
msg.header.fields << Mail::Field.new("X-Mail-Counter: #{count}")

# Output the now modified message back out to $stdout
begin
  $stdout.puts msg.to_s
rescue Errno::EPIPE
  exit(74)
end

Make sure you mark the script executable after saving it.

The only change we need to make from my previous post is to add our ruby mail processor as a procmail filter. I've stored the script in "~/.bin/mail-counter.rb", if you've stored it in a different location you'll want to update your path to reflect that.

Filters in procmail are handled by using the pipe helper. The following is a minimum working example of a "procmailrc" file to make use of our filter:

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MAILDIR=$HOME
VERBOSE=on

:0fw
| /home/sstelfox/Documents/ruby/riak-mail-indexer/counter.rb

:0
Maildir/

Store the above file in "/.procmailrc". The next time you run "fetchmail" those headers will be added to the messages before being delivered and you can watch the count increment by looking at the contents of "/.mail_counter.txt".

The following are a few additional sources I made use of while writing this article: