Rails 3: OpenSSL::SSL::SSLError: hostname was not match with the server certificate

An infinitely better solution (in terms of security that is) than the accepted answer would be:

ActionMailer::Base.smtp_settings = {
  :address              => "mail.foo.com",
  :port                 => 587,
  :domain               => "foo.com",
  :user_name            => "addy@foo.com",
  :password             => "foofoo",
  :authentication       => "plain",
  :enable_starttls_auto => true,
  :openssl_verify_mode  => 'none'
}

This way you’ll still be using encryption, but the validation of the certificate would be disabled (and you won’t be getting any errors).