title: Does RFC 5322 allow reply-to header without any actual e-mail address? If so, what is its semantic?
body: <p><a href="https://www.rfc-editor.org/rfc/rfc5322#section-3.6.2" rel="nofollow noreferrer">Section 3.6.2 of RFC 5322</a> defines the <em>reply-to</em> header as:</p>
  <pre><code>reply-to        =   &quot;Reply-To:&quot; address-list CRLF
  </code></pre>
  <p>Where <em>address-list</em> is defined at <a href="https://www.rfc-editor.org/rfc/rfc5322#section-3.4" rel="nofollow noreferrer">section 3.4</a>. When unfolding the ABNF grammar, I find that <em>address-list</em> can consist of nothing but <code>phrase &quot;:&quot; &quot;;&quot;</code> (<em>phrase</em> being defined at <a href="https://www.rfc-editor.org/rfc/rfc5322#section-3.2.5" rel="nofollow noreferrer">section 3.2.5</a>). So it boils down to you being able to add a <em>reply-to</em> header that does not contains any actual e-mail address.</p>
  <p>The RFC states:</p>
  <blockquote>
  <p>When the &quot;Reply-To:&quot; field is present, it indicates the address(es) to which the author of the message suggests that replies be sent.</p>
  </blockquote>
  <p>Even if it is only a suggestion, it seems rather strange that I can suggest to someone to reply to an address I name but don't specify.</p>
  <p>Am I missing something here? How should I interpret such a construction?</p>