Mailbox Unavailable - not receiving emails from certain recipients

Question

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;

CO1NAM11FT009.mail.protection.outlook.com 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

Answer 1

Hi @William Jones

Do all the users in hotmail.com 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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