ERROR CODE :421 - Host not reachable.

ERROR CODE :421 - Host not reachable.

Hello i have those Emails returned with error :

ERROR CODE :421 - Host not reachable.

 For 2 days it is still happening. 

The full email is:

This message was created automatically by mail delivery software.
A message that you sent could not be delivered to one or more of its recipients. This is a permanent error.

sales@vds-original.com, ERROR CODE :421 - Host not reachable.



Reporting-MTA: dns; mx.zohomail.com
Arrival-Date: Sun, 20 Nov 2022 04:08:34 +0000

Original-Recipient: rfc822; sales@vds-original.com
Final-Recipient: rfc822; sales@vds-original.com
Status: 421
Action: failed
Last-Attempt-Date: 24 Nov 2022 03:56:47 GMT
Diagnostic-Code: Host not reachable.


Received:from vds-original.com (185.27.134.67 [185.27.134.67]) by mx.zohomail.com
    with SMTPS id 1668917317704482.12164568699075; Sat, 19 Nov 2022 20:08:37 -0800 (PST)
Message-ID:<pvvGyUdjIRroa5KFluVinEtUCddhje6NqspHn94q7I@vds-original.com>
Date:Sun, 20 Nov 2022 04:08:34 +0000
From:VDS <Sales@vds-original.com>
To:sales@vds-original.com
Subject:[VDS]: New order #998
Content-Type:text/html; charset=UTF-8

What is the problem?and how to fix it?
thanks