Exchange 2016 - MailFlow issue

Hello Team,

I have problem with Inbound Mail Flow

Scenario
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Two Nodes

Exchange version 2016 with CU11, OS Win 2012

We already have a DAG with 6 nodes , Due to some requirement we had to create a New DAG with 2 nodes

In the New DAG we have 1 DB with a Mailbox

The issue is the Mailbox is able to send emails to other users in the organization ,but not able to receive any emails and they stuck in Queue with error message

[{LED=451 4.4.395 Target host responded with error. - 535 5.7.3 Authentication unsuccessful};{MSG=};{FQDN=Server.domain.net};{IP=10.0.4.40};{LRT=9/16/2019
11:07:30 AM}].

We have checked the default receive connectors and Exchange servers are allowed to connect, Test Mail Flow results shows Failure on both the nodes. Even if the email is sent to mailbox itself its not getting delivered and getting stuck in queue.

Kindly...