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 * Exchange Online Troubleshooting
 * Administration
 * Antispam and protection
 * Calendars
 * Development
 * Email Alias
 * Email Delivery
   * Administrative limit for this request was exceeded error
   * Automatically forward email in transport rule
   * Can't create too large transport rules
   * Can't validate an outbound connector
   * Configure Proofpoint Email Protection with Exchange Online
   * Custom messages are replaced by default system messages
   * Delivery receipts aren't generated for messages sent to external
   * Email sent to EXO deferred with ATTR35
   * Emails aren't received for a new domain
   * Errors when sending/receiving emails
   * External recipients can't get distribution group emails
   * Find and fix email delivery issues
   * How to block message send or receive
   * IMCEAEX non-delivery report
   * Important notice for Microsoft 365
   * Issues with printers, scanners, and LOB apps that send email
   * Length of the property is too long
   * Messages with attachments not delivered
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   * Non-delivery report (NDR)
     * NDR and SMTP errors
     * 450 4.4.317 Cannot connect to remote server [Message=UntrustedRoot]
     * 451 4.7.500-699 (ASxxx)
     * 5.4.6 or 5.4.14
     * 5.7.1. Unable To Relay
     * 550 4.4.7
     * 550 5.0.350
     * 550 x-dg-ref header is too long
     * 550 5.1.0
     * 550 5.1.1 RESOLVER.ADR.ExRecipNotFound
     * 550 5.1.1 through 550 5.1.20
     * 550 5.1.8 Access denied
     * 550 5.1.10
     * 550 5.1.10 RESOLVER.ADR.RecipientNotFound
     * 550 5.1.20 Multiple From addresses
     * 550 5.2.0 RESOLVER.ADR.BadPrimary
     * 550 5.4.1
     * 550 5.6.0 APPROVAL.InvalidExpiry
     * 550 5.6.11
     * 550 5.7.1
     * 550 5.7.12 or 5.7.12
     * 550 5.7.13 or 550 5.7.135
     * 550 5.7.23
     * 550 5.7.57
     * 550 5.7.64
     * 550 5.7.64 TenantAttribution when sending emails externally
     * 550 5.7.64 TenantAttribution when sending emails through EOP
     * 550 5.7.124 or 5.7.124
     * 550 5.7.133
     * 550 5.7.134
     * 550 5.7.136
     * 550 5.7.700 through 550 5.7.750
     * 554 4.3.2 mailbox busy
     * 554 5.2.0 STOREDRV.Deliver.Exception
     * 554 5.2.2 mailbox full
     * 554 5.6.0 Invalid message content
     * AggregateGroupMailbox is full
     * Error 'the sender's submission quota was exceeded'
 * Groups and Distribution Lists
 * Mobile Devices
 * Move/Migrate Mailboxes
 * Outlook Issues
 * Outlook on the web Issues
 * Public Folders
 * Send Emails
 * User and Shared Mailboxes

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FIX NDR ERROR "550 5.1.10" IN EXCHANGE ONLINE

 * Article
 * 2024-01-24
 * 5 contributors

Feedback


IN THIS ARTICLE

    
 1. Why did I get this bounce message?
    
 2. I got this bounce message. How do I fix it?
    
 3. I'm an email admin. How can I fix this issue?
    
 4. Verify the custom domain's mail exchanger (MX) record
    
 5. Still need help with a 5.1.10 bounce message?
    
 6. See also
    

Show 2 more

Important

Mail flow rules are now available in the new Exchange admin center. Try it now!

Problems sending and receiving email messages can be frustrating. If you get a
non-delivery report (NDR), also called a bounce message, for error code 550
5.1.10, this article can help you fix the problem and get your message sent.

Expand table

        I got this bounce message. How do I fix it? I'm an email admin. How can
I fix this issue?


WHY DID I GET THIS BOUNCE MESSAGE?

You received this NDR with error code 5.1.10 for one of the following reasons:

 * The recipient's email address doesn't exist or couldn't be found. Go to the I
   got this bounce message. How do I fix it? section in this article.

Typically, if a message can't be delivered, the recipient's email system will
use the sender's email address in the From field to notify the sender in an NDR
like this one. But what if the message was sent by a spammer who falsified the
From address so it appears the message came from your email address? The
resulting NDR that you'll receive is useless because it creates the false
impression that you did something wrong. This type of useless NDR is called
backscatter. It's annoying, but if this NDR is backscatter, your account hasn't
been compromised.

 * A spammer sent a message to a non-existent recipient, and they falsified the
   From address so it appears the message was sent by your email address. The
   resulting bounce message that you get is called backscatter, and you can
   safely ignore or delete the bounce message.
   
   Backscatter itself is harmless, but if you're getting much of it, it's
   possible that your computer or device is infected with spam-sending malware.
   Consider running an anti-malware scan. Additionally, to help prevent spammers
   from impersonating you or others in your organization, ask your email admin
   to read this topic: Set up SPF to help prevent spoofing.


I GOT THIS BOUNCE MESSAGE. HOW DO I FIX IT?

Here are some steps that you can try to fix the problem yourself.

If the steps in this section don't fix the problem for you, contact your email
admin and refer them to the information in this article so they can try to
resolve the issue for you.


VERIFY RECIPIENT'S EMAIL ADDRESS AND RESEND YOUR MESSAGE

VERIFY RECIPIENT'S EMAIL ADDRESS AND RESEND YOUR MESSAGE IN OUTLOOK

 1. Open the bounce message. In the Report tab, choose Send Again.
    
    
    
    If your original message had an attachment larger than 10 MB, the Send Again
    option might not be available or might not work. Instead, resend the message
    from your Sent Items folder. For more information, see Resend an email
    message.

 2. In the new copy of your message, select the recipient's email address in the
    To box and then press the Delete key.

 3. Remove the recipient's email address from the Auto-Complete list (a bad or
    outdated entry could be causing the problem):
    
    1. In the To box, start typing the recipient's email address until it
       appears in the Auto-Complete drop-down list as shown below.
       
       
    
    2. Use the Down Arrow key to select the recipient from the Auto-Complete
       drop-down list and then press the Delete key or choose the Delete icon to
       the right of the email address.

 4. In the To box, continue typing the entire recipient email address. Be sure
    to spell the address correctly.
    
    
    
    2. Use the Down Arrow key to select the recipient from the Auto-Complete
       drop-down list and then press the Delete key or choose the Delete icon to
       the right of the email address.

 5. In the To box, continue typing the entire recipient email address. Be sure
    to spell the address correctly.

 6. Click Send.

VERIFY RECIPIENT'S EMAIL ADDRESS AND RESEND YOUR MESSAGE IN OUTLOOK ON THE WEB
(FORMERLY KNOWN AS OUTLOOK WEB APP)

 1. Open the bounce message. In the reading pane, just below the message header
    information, choose To send this message again, click here.
    
    
    
    If your original message had an attachment larger than 10 MB, the Send Again
    option might not be available or might not work. Instead, resend the message
    from your Sent Items folder.

 2. On the To line of the new copy of your message, choose the Delete icon to
    delete the recipient's email address.
    
    If your original message had an attachment larger than 10 MB, the Send Again
    option might not be available or might not work. Instead, resend the message
    from your Sent Items folder.

 3. On the To line of the new copy of your message, choose the Delete icon to
    delete the recipient's email address.

 4. Remove the recipient's email address from the Auto-Complete list (a bad or
    outdated entry could be causing the problem):
    
    1. On the empty To line, start typing the recipient's name or email address
       until it appears in the Auto-Complete drop-down list.
       
       
    
    2. Use the Down Arrow key to select the recipient from the Auto-Complete
       list, and then press the Delete key. Or, hover over the recipient's name
       and click the Delete icon .
    
    3. Use the Down Arrow key to select the recipient from the Auto-Complete
       list, and then press the Delete key. Or, hover over the recipient's name
       and click the Delete icon.

 5. On the To line, continue typing the recipient's entire email address. Be
    sure to spell the address correctly.

 6. Click Send.


ASK THE RECIPIENT TO CHECK FOR BROKEN FORWARDING RULES OR SETTINGS

Does the recipient's email address in your original message exactly match the
recipient's email address in the NDR? Compare the recipient's email address in
the NDR with the recipient's email address in the message in your Sent Items
folder.

If the addresses don't match, contact the recipient (by phone, in person, etc.)
and ask them if they've configured an email rule that forwards incoming email
messages from you to another destination. Their rule could have tried to send a
copy of your message to a bad email address. If the recipient has such a rule,
they'll need to correct the destination email address or remove the rule in
order to prevent 5.1.x message delivery errors.

Microsoft 365 and Office 365 support multiple ways to forward messages
automatically. If the intended recipient of your message is using Microsoft 365
or Office 365, ask them to review the Update, disable, or remove Inbox Rules
forwarding and Disable account forwarding sections below.

If the problem persists after performing these steps, ask the recipient to refer
their email admin to the I'm an email admin. How can I fix this issue? section
below.

UPDATE, DISABLE, OR REMOVE INBOX RULES FORWARDING

 1. In Microsoft 365 or Office 365, sign in to your user account.

 2. Click the gear icon in the top-right corner to show the Settings pane.

 3. Select Your app settings > Mail.
    
    

 4. From the Options navigation pane on the left, select Mail > Automatic
    processing > Inbox and sweep rules.
    
    

 5. From the Options navigation pane on the left, select Mail > Automatic
    processing > Inbox and sweep rules.

 6. Update, turn off, or delete any rules that might be forwarding the sender's
    message to a non-existent or broken email address.

DISABLE ACCOUNT FORWARDING

 1. Sign in to your Microsoft 365 or Office 365 account, and from the same
    Options navigation as shown above, select Mail > Accounts > Forwarding.
    
    

 2. Select Stop forwarding and click Save to disable account forwarding.


I'M AN EMAIL ADMIN. HOW CAN I FIX THIS ISSUE?

If the sender can't fix the issue themselves, the problem might be that an email
system on the receiving side isn't configured correctly. If you're the email
admin for the recipient, try one or more of the following fixes and then ask the
sender to resend the message.


VERIFY THAT THE RECIPIENT EXISTS AND HAS AN ACTIVE LICENSE ASSIGNED

To verify that the recipient exists and has an active license assigned:

 1. In the Microsoft 365 admin center, choose Users to go to the Active users
    page.

 2. In the Active users > Filters search field, type part of the recipient's
    name, and then press Enter to locate the recipient. If the recipient doesn't
    exist, then you must create a new mailbox or contact for this user. (For
    more information, see Add users individually or in bulk.) If the recipient
    does exist, make sure the recipient's username matches the email address the
    sender used.
    
    

 3. If the user's mailbox is hosted in Exchange Online, click the user's record
    to review their details and verify that they've been assigned a valid
    license for email (for example, an Office 365 Enterprise E5 license).
    
    

 4. If the user's mailbox is hosted in Exchange Online, but no license has been
    assigned, choose Edit and assign the user a license.
    
    

 5. If the user's mailbox is hosted in Exchange Online, click the user's record
    to review their details and verify that they've been assigned a valid
    license for email (for example, an Office 365 Enterprise E5 license).

 6. If the user's mailbox is hosted in Exchange Online, but no license has been
    assigned, choose Edit and assign the user a license.


FIX OR REMOVE BROKEN FORWARDING RULES OR SETTINGS

Microsoft 365 or Office 365 provides the following features for users and email
admins to forward messages to another email address:

 * Forwarding using Inbox rules (user)

 * Account forwarding (user and email admin)

 * Forwarding using mail flow rules (email admin)

Follow the steps below to fix the recipient's broken mail forwarding rule or
settings.

FORWARDING USING INBOX RULES (USER)

The recipient might have an Inbox rule that is forwarding messages to a
problematic email address. Inbox rules are available only to the user (or
someone with delegated access to their account). See Update, disable, or remove
Inbox Rules forwarding for how the user, or their delegate, can change or remove
a broken forwarding Inbox rule.

ACCOUNT FORWARDING (USER AND EMAIL ADMIN)

 1. In the Microsoft 365 admin center, choose Users.

 2. In the Active users > Filters search field, type part of the recipient's
    name and then press Enter to locate the recipient. Click the user's record
    to view its details.

 3. From the user's profile page, select Mail Settings > Email forwarding >
    Edit.
    
    

 4. Turn off Email forwarding and select Save.
    
    

 5. Turn off Email forwarding and select Save.

FORWARDING USING MAIL FLOW RULES (EMAIL ADMIN)

Unlike Inbox rules that are associated with a user's mailbox, mail flow rules
(also known as transport rules) are organization-wide settings and can only be
created and edited by email admins.

 1. In the Microsoft 365 Admin center, select Admin centers > Exchange.
    
    

 2. In the Exchange admin center (EAC), that is, New EAC or Classic EAC, go to
    Mail flow > Rules.

 3. Look for any redirect rules that might be forwarding the sender's message to
    another address.
    
    * An example of a redirect rule in New EAC is the following image.
      
      
    
    * An example of a redirect rule in Classic EAC is the following image.
      
      

 4. In the Exchange admin center (EAC), that is, New EAC or Classic EAC, go to
    Mail flow > Rules.

 5. Look for any redirect rules that might be forwarding the sender's message to
    another address.
    
    * An example of a redirect rule in New EAC is the following image.
    
    * An example of a redirect rule in Classic EAC is the following image.

 6. Update, turn off, or delete any suspect forwarding rules.

UPDATE ACCEPTED DOMAIN SETTINGS

Notes:

 * Message routing (especially in hybrid configurations) can be complex. Even if
   changing the accepted domain setting fixes the bounce message problem, it
   might not be right solution for you. In some cases, changing the accepted
   domain type might cause other unanticipated problems. Review Manage accepted
   domains in Exchange Online and then proceed with caution.
   
   * If the accepted domain in Exchange Online is Authoritative: The service
     looks for the recipient in the Exchange Online organization, and if the
     recipient isn't found, message delivery stops and the sender will receive
     this bounce message. On-premises users must be represented in the Exchange
     Online organization by mail contacts or mail users (created manually or by
     directory synchronization).
   * If the accepted domain in Exchange Online is Internal Relay: The service
     looks for the recipient in the Exchange Online organization, and if the
     recipient isn't found, the service relays the message to your on-premises
     Exchange Organization (assuming you've correctly set up the required
     connector to do so).

 * When setting an accepted domain to Internal Relay, you must set up a
   corresponding Microsoft 365 or Office 365 connector to your on-premises
   environment. Failing to do so will break mail flow to your on-premises
   recipients. For more information about connectors, see Configure mail flow
   using connectors.

To change the Accepted Domain from Authoritative to Internal Relay:

If you have a hybrid configuration with a Microsoft 365 or Office 365 connector
configured to route messages to your on-premises environment, and you believe
that Internal Relay is the correct setting for your domain, change the Accepted
Domain from Authoritative to Internal Relay.

New Exchange admin center (EAC):

 1. Open the New Exchange admin center (EAC). For more information, see Exchange
    admin center in Exchange Online.

 2. Choose Mail flow > Accepted domains. The Accepted domains screen appears.

 3. Select a recipient's domain and double-click it.
    
    
    
    The accepted's domain details screen appears.

 4. Click the radio button for Internal Relay.
    
    

 5. Click Save.

Classic EAC:

 1. Open the Classic EAC. For more information, see Exchange admin center in
    Exchange Online.

 2. From the EAC, choose Mail flow > Accepted domains and select the recipient's
    domain.
    
    

 3. Double-click the domain name.

 4. In the Accepted Domain dialog box, set the domain to Internal Relay, and
    then select Save.
    
    

MANUALLY SYNCHRONIZE ON-PREMISES AND MICROSOFT 365 OR OFFICE 365 DIRECTORIES

If you have a hybrid configuration and the recipient is located in the
on-premises Exchange organization, it's possible that the recipient's email
address isn't properly synchronized with Microsoft 365 or Office 365. Follow
these steps to synchronize directories manually:

 1. Log into the on-premises server that's running Microsoft Entra Connect Sync.

 2. Open Windows PowerShell on the server and run the following commands:
    
    PowerShell Copy
    
    
    Start-ADSyncSyncCycle -PolicyType Delta
    

When synchronization completes, repeat the steps in the Verify that the
recipient exists and has an active license assigned section to verify that the
recipient address exists in Exchange Online.


VERIFY THE CUSTOM DOMAIN'S MAIL EXCHANGER (MX) RECORD

If you have a custom domain (for example, contoso.com instead of
contoso.onmicrosoft.com), it's possible that your domain's MX record isn't
configured correctly.

 1. In the Microsoft 365 Admin center, go to Settings > Domains, and then select
    the recipient's domain.
    
    

 2. In the pop-out Required DNS settings pane, select Check DNS.
    
    

 3. In the pop-out Required DNS settings pane, select Check DNS.

 4. Verify that there's only one MX record configured for the recipient's
    domain. Microsoft doesn't support using more than one MX record for a domain
    that's enrolled in Exchange Online.

 5. If Microsoft 365 or Office 365 detects any issues with your Exchange Online
    DNS record settings, follow the recommended steps to fix them. You might be
    prompted to make the changes directly within the Microsoft 365 admin center.
    Otherwise, you must update the MX record from your DNS host provider's
    portal. For more information, see Create DNS records at any DNS hosting
    provider.
    
    Note
    
    Typically, your domain's MX record should point to the Microsoft 365 or
    Office 365 fully qualified domain name: <your
    domain>.mail.protection.outlook.com. DNS record updates usually propagate
    across the Internet in a few hours, but they can take up to 72 hours.


STILL NEED HELP WITH A 5.1.10 BOUNCE MESSAGE?








SEE ALSO

Email non-delivery reports in Exchange Online

Backscatter in EOP

Configure email forwarding for a mailbox

Synchronizing your directory with Microsoft 365 or Office 365 is easy

Create DNS records at any DNS hosting provider

Set up SPF to help prevent spoofing





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As a Windows Server hybrid administrator, you integrate Windows Server
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networks.




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 * Previous Versions
 * Blog
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 * Trademarks
 * © Microsoft 2024