Email functionality

Hi All,
  I need my application to have a module with email functionality.
This will have all functionalities of an email client. Each user will
have an inbox, outbox, sent folder, custom folders, sub folders etc.
They should be able to send, receive,forward, reply to emails.

Is there any gem/plugin I can use for this. If there is an
alternative to building this like integration with google apps etc,
please suggest.

Regards,
Pankaj.