Delivery to the following recipient failed permanently:<p><pre><code> inbox@google.com
</code></pre>
Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the server for the recipient domain google.com by aspmx.l.google.com. [2a00:1450:4010:c08::1b].<p>The error that the other server returned was:
550-5.2.1 The user you are trying to contact is receiving mail at a rate that
550-5.2.1 prevents additional messages from being delivered. For more
550-5.2.1 information, please visit
550 5.2.1 http://support.google.com/mail/bin/answer.py?answer=6592 j9si8791583lab.13 - gsmtp
In a big company such as Google with very complex systems, such a thing is likely to happen. Even with very detailed specification with rigid scrutiny, details like this will fall through the cracks. Often we anticipate every possible edge cases but haven't taken into account outside systems that plays a big role too, which leads to cases such as this.