Nothing original here I am afraid.
I copied Google's cache from http://blog.pomozov.info/posts/how-to-send-actionmailer-mails-to-gmailcom.html

1. Save the following code within your rails app in lib/smtp_tls.rb

require "openssl"
require "net/smtp"

Net::SMTP.class_eval do
private
def do_start(helodomain, user, secret, authtype)
raise IOError, 'SMTP session already started' if @started
check_auth_args user, secret, authtype if user or secret

sock = timeout(@open_timeout) { TCPSocket.open(@address, @port) }
@socket = Net::InternetMessageIO.new(sock)
@socket.read_timeout = 60 #@read_timeout
#@socket.debug_output = STDERR #@debug_output

check_response(critical { recv_response() })
do_helo(helodomain)

if starttls
  raise 'openssl library not installed' unless defined?(OpenSSL)
  ssl = OpenSSL::SSL::SSLSocket.new(sock)
  ssl.sync_close = true
  ssl.connect
  @socket = Net::InternetMessageIO.new(ssl)
  @socket.read_timeout = 60 #@read_timeout
  #@socket.debug_output = STDERR #@debug_output
  do_helo(helodomain)
end

authenticate user, secret, authtype if user
@started = true
ensure
unless @started
  # authentication failed, cancel connection.
  @socket.close if not @started and @socket and not @socket.closed?
  @socket = nil
end
end

def do_helo(helodomain)
 begin
  if @esmtp
    ehlo helodomain
  else
    helo helodomain
  end
rescue Net::ProtocolError
  if @esmtp
    @esmtp = false
    @error_occured = false
    retry
  end
  raise
end
end

def starttls
getok('STARTTLS') rescue return false
return true
end

def quit
begin
  getok('QUIT')
rescue EOFError, OpenSSL::SSL::SSLError
end
end
end

2. Add this code to config/environment.rb
   
   require “smtp_tls”

   ActionMailer::Base.smtp_settings = {
   :address => “smtp.gmail.com”,
   :port => 587,
   :authentication => :plain,
   :user_name => “someone@openrain.com”,
   :password => ’someonesPassword’
   }

3. Use ActionMailer as normal.