I got a very good plugin at http://code.google.com/p/capistrano-mailer/.
Just copied the details below to have use in future.

It is a Capistrano Plugin AND a Rails Plugin

Ever wanted to be emailed whenever someone on the team does a cap deploy of trunk or some tag to some server. Wouldn’t it be nice to know about it every time a release was deployed? For large rails projects this type of coordination is essential, and this plugin makes sure everyone on the need to know list is notified when something new is deployed.

This plugin is an extension to Capistrano.

That means it registers itself with Capistrano as a plugin and is therefore available to call in your recipes.

If you are looking to roll your own email integration into capistrano then try this pastie: http://pastie.org/146264 (thanks to Mislav Marohni?). But if you want to take the easy road to riches then keep reading

– figurative “riches” of course, I promise nothing in return for your using this plugin

Requirements

• Rails 2.0.2
• Capistrano 2.1.0 – 2.2.0

Installation

./script/plugin install http://capistrano-mailer.googlecode.com/svn/trunk/capistrano_mailer

Usage

1. Install the plugin.

2. Add this line to the top of your deploy.rb:

require 'vendor/plugins/capistrano_mailer/lib/capistrano_mailer'

3. Add a cap_mailer_settings.rb file to your config/ directory:

require 'vendor/plugins/capistrano_mailer/lib/cap_mailer'

ActionMailer::Base.delivery_method = :smtp
ActionMailer::Base.smtp_settings = {
:address        => "mail.default.com",
:port           => 25,
:domain         => 'default.com',
:perform_deliveries => true,
:user_name      => "releases@default.com",
:password       => "mypassword",
:authentication => :login }
ActionMailer::Base.default_charset = "latin1"

CapMailer.template_root = "vendor/plugins/capistrano_mailer/views/"
CapMailer.recipient_addresses = ["dev1@default.com"]
CapMailer.sender_address = %("Capistrano Deployment" <releases@default.com>)
CapMailer.email_prefix = "[MYSITE-CAP-DEPLOY]"
CapMailer.site_name = "MySite.com"
CapMailer.email_content_type = "text/html"

4. Add these two tasks to your deploy.rb:

namespace :show do
desc "Show some internal Cap-Fu: What's mah NAYM?!?"
task :me do
set :command, task_call_frames.first.task.fully_qualified_name
puts "Running #{command} task"
end
end

namespace :deploy do
...

desc "Send email notification of deployment"
task :notify, :roles => :app do
show.me
mailer.send(rails_env, repository, command, deploy_to, host)
end

...
end

Make sure you’ve defined rails_env, repository, deploy_to and host. command is defined by the show:me task above.

The only required parameters to mailer.send are rails_env, repository, command and deploy_to. The complete set of possible parameters is:

mailer.send(rails_env, repository, command, deploy_to, host = nil, ip_address = nil, output = nil)

If anyone has a cool way of recording the output into a capistrano accessible variable, so that it can be shoved into the release email that would be an excellent contribution!

5. Then add the hook somewhere in your deploy.rb:

after "deploy", "deploy:notify"

6. Enjoy and Happy Capping!