title: Do subdomains protect a domain's reputation when sending emails?
body: <p>I'm working on an application that is meant to distribute emails by the thousands.  We've started interfacing with Mandrill to accomplish this.</p>
  
  <p>So my coworker suggests that we use a subdomain to send all of theses emails out, so as to protect our top-level domain's reputation.  We started squabbling about this because, as I argued, why would a simple subdomain protect our TLD, especially if they both resolve to the same IP address?  If marketing.example.com is sending thousands of emails, aren't spam filters smart enough to know that they really originate from example.com?</p>
  
  <p>So to clarify:</p>
  
  <ul>
  <li>We're currently using Mandrill to distribute mail</li>
  <li>We use DKIM to verify that the domain example.com is the originator of the message</li>
  <li>Right now, we're only using one server to handle all this (plus Mandrill)</li>
  </ul>
  
  <p>So how would switching the sender to marketing.example.com (with matching DKIM) help protect our TLD's reputation as a non-spammer? I don't understand, yet I've read articles to this effect, and he argues fervently that it's the right thing to do, yet no one can tell me <em>how</em> it works.  I understand it from an organizational standpoint, but I don't understand how that protects our domain, unless spam filters really judge rep by the subdomain.</p>
  
  <p>Can someone please help me piece this together?</p>
  
  <p><strong>Edit:</strong></p>
  
  <p>Here are some articles for reference:</p>
  
  <p><a href="http://www.quora.com/Has-anyone-created-a-separate-domain-name-to-send-emails-from-in-order-to-not-jeopardize-their-main-one-We-want-to-be-able-to-communicate-to-clients-without-emails-going-to-spam" rel="noreferrer">Quora Question</a></p>
  
  <p><a href="https://luxsci.com/blog/why-you-should-separate-your-business-and-your-marketing-email-sending.html" rel="noreferrer">LuxSci Blog</a></p>
  
  <p><a href="http://static.mailchimp.com/web/guides/email-delivery-for-it-professionals/package/email-delivery-for-it-professionals.pdf" rel="noreferrer">Mail Chimp Delivery</a> - See page 11</p>