How can I send mail with rails without a template?

In my Rails 3 project, I want to send some simple notification emails. I don't need to make a template for them or do any logic. I just want to fire them off from various places in the system.

If I were doing this in an arbitrary ruby script I would use pony. However, I'd like to still use the rails mail facilities and configuration, so that I get the same reliability and setup that I have for the rest of the mail in my system.

What's the most simple way to do this? Ideally there would be some method like

ActionMailer.send(:to => '[email protected]', :subject =>"the subject", :body =>"this is the body")

The simplest way to send mail in rails 3 without a template is to call the mail method of ActionMailer::Base directly followed by the deliver method,

For ex, the following would send a plain text e-mail:

ActionMailer::Base.mail(
  from: "[email protected]",
  to: "[email protected]",
  subject: "test",
  body: "test"
).deliver

http://api.rubyonrails.org/classes/ActionMailer/Base.html#method-i-mail gives you all the header options and also ideas about the how to send a multipart/alternative email with text/plain and text/html parts directly.

Rails 5 users may find the accepted answer (using format.text {...}) doesn't work; at least I was getting an exception because Rails was looking for a view.

Turns out there's a section in the Rails Guide called Sending Emails without Template Renderingand all one needs to do is supply :content_type and :body options to mail(). E.g.:

class UserMailer < ApplicationMailer
  def welcome_email
    mail(to: params[:user].email,
         body: params[:email_body],
         content_type: "text/html",
         subject: "Already rendered!")
  end
end

Here is little example from Rails Guides which uses render method. I didn't try it, but if it works as render in cotrollers, then you can just use:

render :text => "Your message"

or

render :text => my_message

Where my_message is a parameter.

You can just wrap it in a method which you can call from every place you want.

Updated Rails 3.2.8

In this version of Rails I had to do it like this:

def raw_email( email, subject, body )
  mail(
    :to => email,
    :subject => subject
  ) do |format|
    format.text { render :text => body }
  end
end

You can try something like this:

class Notifier < ActionMailer::Base
  def send_simple_message(options)
    mail(options.except(:body)) do |format|
      format.text { render :text => options[:body] }
    end.deliver
  end
end

For people who land here and need to include ATTACHMENTS, this works:

mail = ActionMailer::Base.mail(
  from: '[email protected]',
  to: '[email protected]',
  subject: 'Interspecies cooperation',
  content_type: "text/html",
  body: 'Yo.'
)
mail.attachments["results.json"] = some_json_string_in_this_case
mail.deliver

Instead of using ActionMailer::Base like in KMG's answer, if you want to use your ApplicationMailer (which may have a default from address already), you can:

ApplicationMailer.new.mail(
  to: '[email protected]',
  subject: 'subject',
  body: 'body'
).deliver