Mailbox Unavailable - not receiving emails from certain recipients

William Jones 1 Reputation point

I am having some problems receiving emails from certain people, most emails are getting throughout one address that it is very important for me to get messages from keeps bouncing back to them with the message; rejected your message to the following email addresses:

xxxx@Karima ben .com
a communication failure occurred during the delivery of this message. Please try to resend the message later. if the problem continues contact your email admin

requested action not taken: mailbox unavailable

(there is a code at the end in brackets but i'm not sure if i should include it here??)

any help appreciated this is very frustrating ! thanks in advance

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A Microsoft programmability model that exposes REST APIs and client libraries to access data on Microsoft 365 services.
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Exchange Server Management
Exchange Server Management
Exchange Server: A family of Microsoft client/server messaging and collaboration software.Management: The act or process of organizing, handling, directing or controlling something.
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  1. Joyce Shen - MSFT 16,646 Reputation points

    Hi @William Jones

    Do all the users in failed to send mails to your tenant or just specific users?

    Does the message include any attachment or any unsafe information? We could try using that account to send a test message to verify the result again.

    In addition, if the issue only occurs on some specific users, we could add them to the whitelist manually. Detailed methods are introduced in the official document: Create safe sender lists in EOP

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