DOMAIN_NOT_RESOLVED

DOMAIN_NOT_RESOLVED

I'm having a problem sending emails to @gtsexpress.com, please help.
Below is the error message received:

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, 27 Jul 2023 21:01:11 -0700
from 

----- The following addresses had fatal errors -----
[@gtsexpress.com]

Message will be retried for 4 more day(s)


Reporting-MTA: dns; mx.zohomail.com
Arrival-Date: Fri, 28 Jul 2023 11:14:04 +0800

Original-Recipient: rfc822; @gtsexpress.com
Final-Recipient: rfc822; @gtsexpress.com
Status: 0
Action: failed
Last-Attempt-Date: 28 Jul 2023 04:01:11 GMT
Diagnostic-Code: DOMAIN_NOT_RESOLVED


Received:from mail.zoho.com by mx.zohomail.com
    with SMTP id 1690514044377941.0768961859586; Thu, 27 Jul 2023 20:14:04 -0700 (PDT)
Message-ID:<1899a7d35b5.11d44ac36657054.6555953163275051631@buyandship.today>
Date:Fri, 28 Jul 2023 11:14:04 +0800

Subject:Test email
Content-Type:multipart/alternative;
    boundary="----=_Part_2142545_2098380142.1690514044343"
User-Agent:Zoho Mail