Diagnostic-Code: 5.4.4 DNS error:NXDOMAIN. Domain not found

Hi, I am getting this error .

Both Sender and Recipients email servers are hosted at Zoho.

All MX record as set well.

we can send from other hosting server.

-----Original Message-----
From: mailer-daemon@mail.zoho.com <mailer-daemon@mail.zoho.com>
Sent: Monday, October 19, 2020 3:40 PM
To: XXXXX@mm-ix.net
Subject: Undelivered Mail Returned to Sender

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.

'XXXXXXX@optimitycomm.com', ERROR CODE :512 - 5.4.4 DNS error:NXDOMAIN. Domain
not found :optimitycomm.com'

Reporting-MTA: dns; mx.zohomail.com
Arrival-Date: Mon, 19 Oct 2020 15:40:13 +0630

Original-Recipient: rfc822; 'XXXX@optimitycomm.com'
Final-Recipient: rfc822; 'XXXXX@optimitycomm.com'
Status: 512
Action: failed
Last-Attempt-Date: 19 Oct 2020 09:10:20 GMT
Diagnostic-Code: 5.4.4 DNS error:NXDOMAIN. Domain not found :optimitycomm.com'

New to Zoho LandingPage?

Access Zoho LandingPage

Zoho LandingPage Resources

New to Zoho Survey?

Access Zoho Survey

Latest Feature Updates

Explore our Pricing & Plans

Zoho Survey Resources

Android Mobile Surveys

Insurvey Blogs

Insight Blogs

Tips & Tricks

New to Zoho CRM Plus?

Deliver unforgettable customer experiences

ACCESS ZOHO CRM PLUS

New to Zoho CRM Plus?

Deliver unforgettable customer experiences

ACCESS ZOHO CRM PLUS

New to Zoho Marketing Plus?

Everything you need to run your marketing

ACCESS ZOHO MARKETING PLUS

New to Zoho Marketing Plus?

Everything you need to run your marketing

ACCESS ZOHO MARKETING PLUS

New to Bigin?

Signup Now

Access Bigin

Latest Feature Updates

Zoho Desk Resources

Desk Community Learning Series
Digest
Functions
Meetups
Kbase
Resources
Glossary
Desk Marketplace
MVP Corner
Word of the Day

Tout forum

France ZUGs

Zoho SalesIQ Resources

Sticky Posts
Open PGP integration with Zoho Mail is now here!
Hello Community, We're in much delight to announce that the long awaited integration of Open PGP with Zoho Mail is now released to users in US, EU, AU and IN DCs. With this integration. you can now send out encrypted and digitally signed emails which
Free Webinar Alert! Transform your digital work experience with Zoho Workplace and Zoho Sign
Hello Community!!! We're excited to announce the free webinar on Transforming your digital work experience with Zoho Workplace apps and Zoho Sign integration! Join us for the webinar! Click here, to register!
Announcing ZUG Australia & New Zealand Meet-ups - Meet, Talk, and Learn from Workplace Experts!
Hello Everyone! Our Workplace experts are visiting the top cities in Australia & New Zealand to meet you all in person and help you boost the productivity of your organisation. Come and meet us at one of the cities listed below - whichever is nearer to
Announcing ZUG New Zealand Meet-ups in Auckland, Wellington & Brisbane - Meet, Talk, and Learn from Workplace Experts!
Hello Everyone! Our Workplace experts are visiting the top cities in New Zealand to meet you all in person and help you boost the productivity of your organisation. Come and meet us at Auckland, Wellington or Christchurch - whichever is nearer to you.
Announcing ZUG Australia Meet-ups in Melbourne, Sydney & Brisbane - Meet, Talk, and Learn from Workplace Experts!
Hello Everyone! Our Workplace experts are visiting the top cities in Australia to meet you all in person and help you boost the productivity of your organisation. Come and meet us at Melbourne, Sydney or Brisbane - whichever is nearer to you. Find our