MTA dns; mx.zohomail.com

MTA dns; mx.zohomail.com

Zoho Help Desk Team,

We are getting the below bounce back when replying to tickets within ZOHO. How do we resolve?

This message was created automatically by mail delivery system.

THIS IS A WARNING MESSAGE ONLY.

YOU DO NOT NEED TO RESEND YOUR MESSAGE.

The original message was received at Thu, 02 Jun 2022 14:36:27 -0700
from support@********.zohodesk.com [********.com]

----- The following addresses had fatal errors -----
[stephani********.com, ********.com]

Message will be retried for 4 more day(s)


Reporting-MTA: dns; mx.zohomail.com
Arrival-Date: Thu, 02 Jun 2022 13:50:45 -0700

Original-Recipient: rfc822; ********.com
Final-Recipient: rfc822; ********.com
Status: 421
Action: failed
Last-Attempt-Date: 2 Jun 2022 21:36:27 GMT
Diagnostic-Code: Host not reachable.

Original-Recipient: rfc822; ********.com
Final-Recipient: rfc822; ********.com
Status: 421
Action: failed
Last-Attempt-Date: 2 Jun 2022 21:36:27 GMT
Diagnostic-Code: Host not reachable.


Received:from mail.zoho.com by mx.zohomail.com
    with SMTP id 16542030*******.****28511; Thu, 2 Jun 2022 13:50:45 -0700 (PDT)
Message-ID:
Date:Thu, 02 Jun 2022 13:50:45 -0700
From:******* <********.com>
To:"*******" <********.com>
Cc:"*******" <********.com>
Subject:Re:[## 8376 ##] user activate
Content-Type:multipart/alternative;
    boundary="----=_Part_2728358_840513595.1654203045388"
User-Agent:Zoho Mail