title: Can't remove a mailbox
body: <p>I've got a mailbox that I wish to remove. However the error message I get is as follows.</p>
  
  <blockquote>
    <p>The mailbox associated to a user or a queue cannot be deleted.</p>
  </blockquote>
  
  <p>However, I can't see what user/queue that might be locking it. The only thing I can think of is the <em>Regarding</em> lookup but it's disabled and can't be set to anything else...</p>
  
  <p>We have a new person on a team and I told them to go nuts but those nuts they've created are weird because I can't see how to remedy that (if the issue's got to do with <em>Regarding</em> at all...)</p>
  
  <p>I've tried activating/deactivating, resending the test mail, adding/removing a server profile etc. Mor eor less, anything that I could... The only hit that I found of value (and that's an exaggeration) was <a href="https://community.dynamics.com/crm/f/117/t/143832.aspx" rel="nofollow noreferrer">some guy's vague suggestions</a>...</p>
  
  <p><img src="https://i.stack.imgur.com/COLIc.png" alt="enter image description here"></p>