Errors sending emails via mailgun
<p>A few of the emails being sent from my account are getting rejected. These are the error messages:</p>

<ol>
<li>Server response: 550 550 Requested action not taken: mailbox unavailable invalid DNS MX or A/AAAA resource record</li>
<li>From: Domain is invalid. Please provide a valid From: IB506 <a href="http://x.co/srbounce">http://x.co/srbounce</a></li>
</ol>

<p>Is this issue on my end or their (the receivers) end? How should I fix this problem?</p>