title: 450 error when sending email through IIS, SMTP
body: <p>One of our servers is running a website that sends out email addresses with
  logins and passwords upon a user's registration. The email is configured with CDO. We seem to be getting blocked by some email services (see below). Is there a way to configure either rDNS, DNS, PTR, or SPF records to avoid getting bounce-backs?</p>
  
  <p>Our company's public IP is x.x.x.195</p>
  
  <p>The IIS server name is Server1a; private domain is private.com</p>
  
  <p>The site it is sending from is public.com; public IP is x.x.x.140</p>
  
  <p>We are getting bouncebacks from ATT, AOL, and other email services. Here is an
  example of one: </p>
  
  <p>Message delivery to the host '204.127.217.21' failed while delivering to the
  remote domain 'att.net' for the following reason: An SMTP protocol error
  occurred.
   The SMTP verb which caused the error is 'MAIL'.  The response from the remote
  server is '450 service permits 2 unverifyable sending IPs - server1a.private.com
  is not x.x.x.195</p>