How to include full-path in Rails 3 link_to statement?

I am trying to put a Rails link_to statement inside a Mailer email that includes the full-path (ie - http://localhost/contacts/id/confirm). The link_to statement that I am trying works in my standard View in /pages/options, but not in the Mailer email.

Here is my /pages/options Controller code:

class PagesController < ApplicationController
    def options
    end
end

And here's the pages/options View:

<div>
    <%= link_to "here", :controller => "contacts", :action => "confirm", 
    :only_path => false, :id => 17 %>
</div>

When I put this link into the following mailer (welcome_email.html.rb), I am getting the error below. Any help with this will be greatly appreciated.

<!DOCTYPE html>
<html>
<head>
    <meta content="text/html; charset=UTF-8" http-equiv="Content-Type" />
</head>
<body>
    <%= link_to "here", :controller => "contacts", :action => "confirm",
     :only_path => false, :id => 17 %>
</body>
</html>

The error message:

RuntimeError in Contacts#create

Showing C:/Documents and Settings/Corey Quillen/My Documents/Dev/Dev    
Projects/my_project
Project/my_project/app/views/user_mailer/welcome_email.html.erb where line #7  
raised:

Missing host to link to! Please provide :host parameter or set  
default_url_options[:host]
Extracted source (around line #7):

4:     <meta content="text/html; charset=UTF-8" http-equiv="Content-Type" />
5:   </head>
6:   <body>
7:     <%= link_to "here", :controller => "contacts", :action => "confirm", :only_path    
=> false, :id => 17 %>
8:   </body>
9: </html>