how to generate a link like link_to on mailer?

I used rails mailer to send a email to my client, but soon I found I
can't use link_to on mailer.
the effect I want is like this.
<a href="http://localhost.com/great">great</a>

so, any thought here?

From http://guide.rails.info/action_mailer_basics.html#using-action-mailer-helpers
helper_method :link_to def link_to(name, options)

Regards,
Jason Stewart