configuring an object inheriting from actionmailer

I've been attempting to create a simple postback script using ruby, one
that takes what is sent to it (cgi) and emails it out (action mailer). I
ran into some problems (cgi values weren't coming through whenever I
required action mailer) early on using the two of these as follows:

require "cgi"
require "rubygems"
require "action_mailer"

Rolling back to actionmailer 1.3.6 fixed those problems. I've since
found that using the two as follows also allows the cgi values to come
through using the latest action mailer:

require "cgi"
require "rubygems"
gem "actionmailer"

However, I can't figure out how to configure the object inheriting from
action mailer when I use gem "actionmailer".

I used to do this:

ActionMailer::Base.delivery_method = :smtp

But that give me an uninitialized constant error on ActionMailer. How
can I configure these options now?