Unable to send email to specific domain

ATFRMZ 41 Reputation points

We have Exchange2016 Hybrid setup and I am experiencing following error:

Server at b.domain.com (x.x.x.x) returned '400 4.4.7 Message delayed'
11/20/2022 5:43:18 PM - Server at b.domain.com (x.x.x.x) returned '451 4.4.397 Error communicating with target host. -> 421 4.2.1 Unable to connect -> SocketTimedout: Socket error code 10060'

Please advise.

Microsoft Exchange Online Management
Microsoft Exchange Online Management
Microsoft Exchange Online: A Microsoft email and calendaring hosted service.Management: The act or process of organizing, handling, directing or controlling something.
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  1. Aholic Liang-MSFT 13,826 Reputation points Microsoft Vendor

    Hi @ATFRMZ ,
    Are you getting this error when you mails to other domains?
    If this error only occurs when sending to the same domain, the issue is caused by their server's settings(b.contoso.com).Therefore, we recommend that you contact their administrator to allow receiving your messages.

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