Mailer interceptor

gistfile1.rb

#config/initializers/interceptor.rb
require "#{Rails.root}/lib/development_mail_interceptor"
ActionMailer::Base.register_interceptor(DevelopmentMailInterceptor) if Rails.env.development?

#lib/development_mail_interceptor.rb
class DevelopmentMailInterceptor
  def self.delivering_email(message)
    message.subject = "[#{message.to}] #{message.subject}"
    message.to = `git config --global user.email`.strip
  end  
end