How to resolve Recipient Address Rejected issue

John Kelly 146 Reputation points


We have an Exchange hybrid set up and we have a shared mailbox that people external to our organisation get an NDR message when they try to send to it.

The message is 554: 5.7.1 Recipient address rejected: Access denied

Users internal can send to this email address.

We have a number of Shared Mailboxes that all work okay but i think this one has been set up directly in the Office 365 Exchange Admin Portal

When we are creating a shared mailbox we normally create these in the on premise hybrid server (ECP) and then migrate this to Office 365. The mailbox then shows in the hybrid server (ECP) and also the Office 365 portal.

This failing email address is only showing in the Office 365 Exchange Admin portal and not on hybrid server.

Can anyone offer any advice on how to resolve this please


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.
7,440 questions
Microsoft Exchange Hybrid Management
Microsoft Exchange Hybrid Management
Microsoft Exchange: Microsoft messaging and collaboration software.Hybrid Management: Organizing, handling, directing or controlling hybrid deployments.
1,960 questions
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Accepted answer
  1. Courtny Cotten 86 Reputation points Microsoft Employee

    It sounds like the issue might be related to the permissions or configuration settings for the shared mailbox in question. Here are a few troubleshooting steps you can try:

    1. Check the mailbox settings: Make sure that the external sharing settings for the shared mailbox are configured correctly. In the Exchange admin center, go to Recipients > Shared and verify that the shared mailbox is configured to allow external sharing.
    2. Check the mailbox permissions: Verify that the external users have the necessary permissions to send email to the shared mailbox. In the Exchange admin center, go to Recipients > Shared, select the shared mailbox, and click Edit. Check the permissions assigned to the mailbox and make sure that external users have the necessary permissions to send email.
    3. Check the spam filter settings: It's possible that the NDR message is being triggered by a spam filter. Check the spam filter settings to make sure that the shared mailbox is not being blocked.
    4. Check the hybrid configuration: Since the shared mailbox is not showing up on the hybrid server, it's possible that there is an issue with the hybrid configuration. Check the hybrid configuration settings to make sure that the shared mailbox is being synchronized correctly.
    5. Verify DNS settings: Ensure that the external email is properly resolved and directed to the organization. Check your domain name system (DNS) settings, including MX, A, CNAME, and SPF records to confirm if the shared mailbox’s domain is correctly configured.

    Hopefully, one of these steps will help resolve the issue. If not, you may need to investigate further or reach out to Microsoft Support for additional assistance.

    Answer generated with AI assistance from ChatGPT

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2 additional answers

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  1. Jame Xu-MSFT 4,171 Reputation points

    Hi @John Kelly ,

    Are all external users unable to send emails to this shared mailbox? Is it normal for external users to send emails to other shared mailboxes? Possible reasons are that the user IP is in the blacklist or is blocked.

    The error code "554 5.7.1" is a common error, the following article has summarized the reasons about this error, check if any helps: The 554 5.7.1 SMTP error

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  2. John Kelly 146 Reputation points


    I was out office and just getting back to this issue which has now been resolved and thank you both for your input.

    I used Courtney troubleshooting steps and his Item 4 suggestion pointed me in the right direction. The person that had created this shared mailbox had created it on Office 365 only.

    I deleted this and created a user in AD and a mailbox on the hybrid Exchange.

    I migrated this to Office 365 and then converted it to a shared mailbox and was able to receive emails to this from external emails.



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