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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
   * NDR when external users send email to a Microsoft 365 group
   * 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
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 * Groups and Distribution Lists
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 * Outlook Issues
 * Outlook on the web Issues
 * Public Folders
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FIX NDR ERROR CODE "550 5.1.1" THROUGH "550 5.1.20" IN EXCHANGE ONLINE

 * Article
 * 01/23/2024
 * 5 contributors

Feedback


IN THIS ARTICLE

    
 1. I got this bounce message. How do I fix it?
    
 2. I'm an email admin. What can I do to fix this?
    
 3. Still need help with error code 5.1.1 to 5.1.20?
    
 4. See also
    

Important

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

It's frustrating when you get an error after sending an email message. This
article describes what you can do if you see error codes 550 5.1.1 through
5.1.20 in a non-delivery report (also known as an NDR, bounce message, delivery
status notification, or DSN).

Expand table

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


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.


SOLUTION 1: CONFIRM THE RECIPIENT'S EMAIL ADDRESS

It sounds too simple, but the wrong email address is the most common issue that
causes 5.1.x errors. Check for correct spelling and send the message again if
you find an error in the email address.

To resend the message in Outlook, see Resend an email message.


SOLUTION 2: REMOVE THE RECIPIENT'S EMAIL ADDRESS FROM YOUR AUTO-COMPLETE LIST

You might have an invalid entry in your Auto-Complete list (also known as the
nickname cache) for the recipient. For example, the recipient might have been
moved from an on-premises Exchange organization to Exchange Online, or
vice-versa. Although the recipient's email address is the same, other internal
identifiers for the recipient might have changed, thus breaking your cached
entry for the recipient.

FIX YOUR AUTO-COMPLETE LIST ENTRIES IN OUTLOOK

To remove invalid recipients or all recipients from your Auto-Complete list in
Outlook 2010 later, see Manage suggested recipients in the To, Cc, and Bcc boxes
with Auto-Complete.

FIX YOUR AUTO-COMPLETE LIST ENTRIES IN OUTLOOK ON THE WEB

To remove recipients from your Auto-Complete list in Outlook on the web
(formerly known as Outlook Web App), do one of the following procedures:

REMOVE A SINGLE RECIPIENT FROM YOUR OUTLOOK ON THE WEB AUTO-COMPLETE LIST

 1. In Outlook on the web, click New mail.

 2. Start typing the recipient's name or email address in the To field until the
    recipient appears in the drop-down list.
    
    

 3. Use the Down Arrow and Up Arrow keys to select the recipient, and then press
    the Delete key.

REMOVE ALL RECIPIENTS FROM YOUR OUTLOOK ON THE WEB AUTO-COMPLETE LIST**

You can only clear your Auto-Complete list in the light version of Outlook on
the web. To open your mailbox in the light version of Outlook on the web, do
either of the following steps:

 * Open the mailbox in an older web browser that only supports the light version
   of Outlook on the web (for example, Internet Explorer 9).

 * Configure your Outlook on the web settings to only use the light version of
   Outlook on the web (the change takes effect the next time you open the
   mailbox):
   
   1. In Outlook on the web, click Settings .
   
   2. In the Search all settings box, type light and select Outlook on the web
      version in the results.
   
   3. In the page that opens, select Use the light version of Outlook on the
      web, and then click Save.
   
   4. Log off, close your web browser, and open the mailbox again in Outlook on
      the web.

After you open your mailbox in the light version of Outlook on the web, do the
following steps to clear all entries from your Auto-Complete list:

 1. Choose Options and verify that Messaging is selected.

 2. In the E-Mail Name Resolution section, click Clear Most Recent Recipients
    list, and then click OK in the confirmation dialog box.

 3. While you're still in Options, to return your mailbox to the full version of
    Outlook on the web, go to Outlook version, clear the check box for Use the
    light version, and then click Save.

 4. Log off and close your web browser. The next time you open your mailbox in a
    supported web browser, you'll use the full version of Outlook on the web.

To remove invalid recipients or all recipients from your Auto-Complete list in
Outlook 2010 later, see Manage suggested recipients in the To, Cc, and Bcc boxes
with Auto-Complete.


SOLUTION 3: CONFIRM THAT THE RECIPIENT ISN'T AUTO-FORWARDING MESSAGES FROM YOU
TO ANOTHER (AND LIKELY, INVALID) EMAIL ADDRESS

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.


SOLUTION 4: VERIFY THAT YOUR ACCOUNT HASN'T BEEN COMPROMISED

Did you send the original message at all? If not, it's possible that a spammer
or hacker inappropriately used your account to send the message.

Check your recent messages in the Sent Items folder for strange or unknown
messages (messages that you didn't send). If you find any, it's possible that
your email account was compromised.

If you believe that your account has been compromised, follow these steps:

 * Reset your password and scan your devices for malware. However, the hacker
   might have configured other settings on your mailbox (for example, created
   Inbox rules to auto-forward email messages or added additional mailbox
   delegates). So, follow the additional steps in Responding to a compromised
   account.

 * Notify your email admin. Your admin will need to unblock your account before
   you can send email again.


SOLUTION 5: CONFIRM THAT THE NDR IS RELATED TO A MESSAGE THAT YOU ACTUALLY SENT

If your Sent folder contains only messages that you know you sent, then the NDR
you received could be a result of backscatter (a useless NDR about a message you
didn't send), and you can ignore it.

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.

Check your recent messages in the Sent Items folder for strange or unknown
messages (messages that you didn't send). If you don't see any suspicious
messages, it's likely that the NDR you received is backscatter. If you've
already changed your password and run an anti-malware scan, you can ignore these
backscatter NDRs.

To learn more, see Backscatter in EOP.


I'M AN EMAIL ADMIN. WHAT CAN I DO TO FIX THIS?

If the steps in the previous section don't solve the issue for the sender, the
solution might be related to the way the user's Microsoft 365 or Office 365
account is set up. If you have a hybrid topology, the solution might also be
related to the on-premises mail transfer agent. It might also be a problem with
the recipient's domain configuration. Here are four solutions you can try. You
might not need to try all of them to get the message sent successfully.


SOLUTION 1: CHECK THE MICROSOFT 365 ADMIN CENTER FOR CONFIGURATION PROBLEMS OR
SERVICE-WIDE ISSUES

For Microsoft 365 or Office 365 accounts, the Microsoft 365 admin center
provides a central source for various tools, notifications, and information that
you can use to troubleshoot this and other issues.

Open the Microsoft 365 admin center, and from the Home page, do the following
items:

 1. Check the Message Center to see if your organization has a known
    configuration issue.

 2. Go to Health > Service health to see if there's a current service issue in
    Microsoft 365 or Office 365 affecting the user's account.

 3. Check the sender and recipient domains for incorrect or stale mail exchange
    (MX) resource records by running the Mailflow Troubleshooter tool that is
    available within Microsoft 365 and Office 365.

If there's a problem with the recipient's domain, contact the recipient or the
recipient's email administrator to let them know about the problem. They'll have
to resolve the issue in order to prevent NDR 5.1.x errors.


SOLUTION 2: UPDATE STALE MX RECORDS

Error code 5.1.1 can be caused by problems with the MX resource record for the
recipient's domain. For example, the MX record might point to an old email
server, or the MX record might be ambiguous due to a recent configuration
change.

Note

Updates to a domain's DNS records can take up to 72 hours to propagate to all
DNS servers on the Internet.

If external senders (senders outside your organization) receive this NDR when
they send message to recipients in your domain, try the following steps:

 * The MX resource record for your domain might be incorrect. The MX record for
   an Exchange Online domain points to the email server (host)
   <domain>.mail.protection.outlook.com.

 * Verify that you have only one MX record configured for your Exchange Online
   domain. We don't support using more than one MX record for domains enrolled
   in Exchange Online.

 * Test your MX record and your ability to send email from your Exchange Online
   organization by using the Verify MX Record and Outbound Connector Test at
   Office 365 > Mail Flow Configuration in the Microsoft Remote Connectivity
   Analyzer.

For more information, see Add DNS records to connect your domain and Set up SPF
to help prevent spoofing.


SOLUTION 3: UPDATE FORWARDING RULES TO REMOVE INCORRECT EMAIL ADDRESSES

This NDR might be caused by a forwarded (unintended) recipient that's configured
for the intended recipient. For example:

 * A forwarding Inbox rule or delegate that the recipient configured in their
   own mailbox.

 * A mail flow rule (also known as a transport rule) configured by an email
   admin that copies or forwards messages sent to the recipient to another
   invalid recipient.

For more information, see Configure email forwarding for a mailbox.


STILL NEED HELP WITH ERROR CODE 5.1.1 TO 5.1.20?








SEE ALSO

Email non-delivery reports in Office 365





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Training

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Examine email protection in Microsoft 365 - Training

This module examines how Exchange Online Protection (EOP) protects organizations
from phishing and spoofing. It also explores how EOP blocks spam, bulk email,
and malware before they arrive in users’ mailboxes.




IN THIS ARTICLE



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