Fix email delivery issues for error code 5.7.136 in Exchange Online

It's frustrating when you get an error after sending an email message. This topic describes what you can do if you see error code 550 5.7.136 in a non-delivery report (also known as an NDR, bounce message, delivery status notification, or DSN). You'll see this automated notification when the recipient is a mail user that's configured to reject messages from external senders (senders from outside the organization).

Email user icon I got this bounce message. How do fix it? Email admin icon I'm an email admin. How do I fix this?

I got this bounce message. How do I fix it?

Only an email admin in the recipient's organization can fix this issue. Contact the email admin and refer them to this information so they can try to resolve the issue for you.

I'm an email admin. How do I fix this?

The two methods that will allow an external sender to send messages to the mail user in your organization are described in the following sections.

To open the Exchange admin center (EAC), see Exchange admin center in Exchange Online.

Method 1: Allow all internal and external senders to send messages to this mail user

  1. In the EAC, go to Recipients > Contacts > select the mail user from the list, and then click Edit Edit icon.

    View contacts to help fix DSN 5.7.136

  2. In the mail user properties dialog box that opens, go to Mailbox flow settings and then click View details in the Message Delivery Restrictions section.

  3. In the Message delivery restrictions dialog box that opens, configure the following settings in the Accept messages from section:

    • Clear the check box for Require that all senders are authenticated.

    • Select Only senders in the following list, and then click Add Add icon. In the Select Members dialog box that opens, select and add the external senders and the all internal users group. When you're finished, click OK.

      Steps to solve DSN 5.7.136 and manage recipient settings

  4. Click OK, and then click Save.

Method 2: Use the mail user's allowed senders list

Instead of allowing all external senders to send messages to this mail user, you can use the mail user's allowed senders list to selectively allow messages from all internal senders and the specified external senders.

Notes:

  • To add an external sender to a mail user's allowed senders list, you must first create a mail contact or a mail user to represent the external sender in your organization.

  • To add everyone in your organization to a mail user's allowed sender's list, you can create a distribution group or a dynamic distribution group that contains everyone in your organization. After you create this group, you can add it to the mail user's allowed senders list.

  • The mail user's allowed senders list is completely different from the organization's allowed senders list for anti-spam that you manage in the EAC at Protection > Spam filter.

To configure the mail user's allowed senders list, open the EAC do the following steps:

  1. In the EAC, go to Recipients > Contacts > select the mail user from the list, and then click Edit Edit icon.

    View contacts to help fix DSN 5.7.136

  2. In the mail user properties dialog box that opens, go to Mailbox flow settings and then click View details in the Message Delivery Restrictions section.

  3. In the Message delivery restrictions dialog box that opens, configure the following settings in the Accept messages from section:

    • Clear the check box for Require that all senders are authenticated.

    • Select Only senders in the following list, and then click Add Add icon. In the Select Members dialog box that opens, select and add the external senders and the all internal users group. When you're finished, click OK.

      Add an allowed sender in the Admin center to help solve DSN 5.7.136

  4. Click OK, and then click Save.

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See also

Email non-delivery reports in Exchange Online