title: Recipient address rejected: Message rejected due to: SPF fail - not authorized
body: <p>I company wants to send email to us, but it gets bounced back with the error </p>
  
  <pre><code>"Your message wasn't delivered due to a permission or security issue. It may have been rejected by a moderator, the address may only accept email from certain senders, or another restriction may be preventing delivery. Recipient address rejected: Message rejected due to: SPF fail - not authorized."
  </code></pre>
  
  <p>I've checked our records and theirs in <a href="https://mxtoolbox.com" rel="nofollow noreferrer">https://mxtoolbox.com</a> and get no obvious errors. Now I'm stuck. Any advice as to what else to check?</p>