Fix NDR error "550 5.7.134" 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 5.7.134 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 mailbox that's configured to reject messages from external senders (senders from outside the organization).
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I got this bounce message. How do I fix this issue? | 
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I'm an email admin. How do I fix this issue? |
I got this bounce message. How do I fix this issue?
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 issue?
The two methods that will allow an external sender to send messages to the mailbox in your organization are described in the following sections.
To open the New Exchange admin center (EAC), see Exchange admin center in Exchange Online.
To open the Classic EAC, click Classic Exchange admin center on the left pane of the Exchange admin center (New) home screen, as shown in the image below.
Method 1: Allow all internal and external senders to send messages to this mailbox
New EAC
Go to Recipients > Mailboxes.
Select a user mailbox from the list and click it. The user mailbox properties screen appears.
Under Mail flow settings, click Manage mail flow settings. The Manage mail flow settings screen appears.
In the Message delivery restriction pane, click Edit. The Message delivery restrictions screen appears.
Under Accept messages from, clear the check box for Require senders to be authenticated.
Click Save.
Classic EAC
In the Classic EAC, go to Recipients > Mailboxes > select the mailbox from the list, and then click Edit
.
In the mailbox properties dialog box that opens, go to Mailbox features > Message Delivery Restrictions > and then click View details.
In the Message delivery restrictions dialog box that opens, clear the check box for Require that all senders are authenticated in the Accept messages from section.
Click OK, and then click Save.
Method 2: Use the mailbox's allowed senders list
Instead of allowing all external senders to send messages to this mailbox, you can use the mailbox'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 mailbox'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 mailbox'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 mailbox's allowed senders list.
- The mailbox's allowed senders list is different from the organization's allowed senders list for anti-spam that you manage in the EAC at Protection > Spam filter.
To configure the mailbox's allowed senders list, do the following steps:
New EAC
Go to Recipients > Mailboxes.
Select a user mailbox from the list and click it. The user mailbox properties screen appears.
Under Mail flow settings, click Manage mail flow settings. The Manage mail flow settings screen appears.
In the Message delivery restriction pane, click Edit. The Message delivery restrictions screen appears.
Under Accept messages from:
Clear the check box for Require senders to be authenticated.
Select Selected senders.
Click + Add sender. The Accept messages from screen appears.
Check the check boxes of the internal-senders group and the specific external users you want to add.
Click Confirm.
The Message delivery restrictions screen reappears.
Click Save.
Classic EAC
In the Classic EAC, go to Recipients > Mailboxes > select the mailbox from the list, and then click Edit
.
In the mailbox properties dialog box that opens, go to Mailbox features > Message Delivery Restrictions > and then click View details.
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
. In the Select Members dialog box that opens, select the external senders and the "all internal users" group.Add the external senders and the "all internal users" group.
When you're finished, click OK.
Click OK, and then click Save.
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