Email non-delivery reports and SMTP errors in Exchange Online (2023)

4324.3.2STOREDRV.Deliver; recipient thread limit exceededThe recipient mailbox's ability to accept messages is being throttled because it's receiving too many messages too quickly. This is done so a single recipient's mail processing doesn't unfairly impact other recipients sharing the same mailbox database.For more information about this by-design throttling, see Store Driver Fault Isolation Improvements in Exchange 2010 SP1.4.4.316Connection refused [Message=Socket error code 10061]Microsoft 365 or Office 365 is trying to send a message to an email server outside of Microsoft 365 or Office 365, but attempts to connect to it are failing due to a network connection issue at the external server's location.This error almost always indicates an issue with the receiving server or network outside of Microsoft 365 or Office 365. The error should also include the IP address of the server or service that's generating the error, which you can use to identify the party responsible for fixing this.4.4.7Message expiredThe message in the queue has expired. The sending server tried to relay or deliver the message, but the action wasn't completed before the message expiration time occurred. This message can also indicate that a message header limit has been reached on a remote server, or some other protocol time-out occurred while communicating with the remote server.This message usually indicates an issue on the receiving server. Check the validity of the recipient address, and determine if the receiving server is configured correctly to receive messages.

You might have to reduce the number of recipients in the message header for the host about which you're receiving this error. If you send the message again, it's placed in the queue again. If the receiving server is available, the message is delivered.

For more information, see Fix email delivery issues for error code 4.4.7 in Exchange Online.

4.5.3Too many recipientsThe message has more than 200 SMTP envelope recipients from the same domain.An envelope recipient is the original, unexpanded recipient that's used in the RCPT TO command to transmit the message between SMTP servers. When this error is returned by Microsoft 365 or Office 365, the sending server must break up the number of envelope recipients into smaller chunks (chunking) and resend the message.4.7.26Access denied, a message sent over IPv6 [2a01:111:f200:2004::240] must pass either SPF or DKIM validation, this message is not signedThe sending message sent over IPv6 must pass either SPF or DKIM.For more information, see Support for anonymous inbound email messages over IPv6.4.7.321starttls-not-supported: Destination mail server must support TLS to receive mail.DNSSEC checks have passed, yet upon connection, destination mail server doesn't respond to the STARTTLS command.

The destination server responds to the STARTTLS command, but the TLS handshake fails.

This message usually indicates an issue on the destination email server. Check the validity of the recipient address. Determine if the destination server is configured correctly to receive the messages.4.7.322certificate-expired: Destination mail server's certificate is expired.DNSSEC checks have passed, yet upon establishing the connection, the destination mail server provides a certificate that is expired.A valid X.509 certificate that isn't expired must be presented. X.509 certificates must be renewed after their expiration, commonly annually.4.7.323tlsa-invalid: The domain failed DANE validation.Records are DNSSEC authentic, but one or multiple of these scenarios occurred:

• The destination mail server's certificate doesn't match with what is expected per the authentic TLSA record.
• Authentic TLSA record is misconfigured.
• Destination domain is being attacked.
• Any other DANE failure.

This message usually indicates an issue on the destination email server. Check the validity of recipient address and determine if the destination server is configured correctly to receive messages. For more information, see DANE protocol: updates and operational guidance4.7.324dnssec-invalid: Destination domain returned invalid DNSSEC recordsThe destination domain indicated it was DNSSEC-authentic, but Exchange Online wasn't able to verify it as DNSSEC-authentic.For more information, see Overview of DNSSEC.4.7.325certificate-host-mismatch: Remote certificate MUST have a common name or subject alternative name matching the hostname (DANE)This happens when the presented certificate identities (CN and SAN) of a destination SMTP target host don't match any of the domains or MX host.This message usually indicates an issue on the destination email server. Check the validity of recipient address and determine if the destination server is configured correctly to receive messages. For more information, see How SMTP DNS-based Authentication of Named Entities (DANE) works to secure email communications.4.7.500-699Access denied, please try again laterSuspicious activity has been detected and sending has been temporarily restricted for further evaluation.If this activity is valid, this restriction will be lifted shortly.4.7.850-899Access denied, please try again laterSuspicious activity has been detected on the IP in question, and it has been temporarily restricted while it's being further evaluated.If this activity is valid, this restriction will be lifted shortly.5.0.350Generic error, x-dg-ref header is too long, or Requested action not taken: policy violation detected (AS345)5.0.350 is a generic catch-all error code for a wide variety of non-specific errors from the recipient's email organization. The specific x-dg-ref header is too long message is related to Rich Text formatted messages. The specific Requested action not taken: policy violation detected (AS345) message is related to nested attachments.For more information, see Fix email delivery issues for error code 550 5.0.350 in Exchange Online.5.1.0Sender deniedA common cause of this NDR is when you use Microsoft Outlook to save an email message as a file, and then someone opened the message offline and replied to it. The message property only preserves the legacyExchangeDN attribute when Outlook delivers the message, and therefore the lookup could fail.Either the recipient address is incorrectly formatted, or the recipient couldn't be correctly resolved. The first step in resolving this error is to check the recipient address, and send the message again.

For more information, see Fix email delivery issues for error code 5.1.0 in Exchange Online.

5.1.1Bad destination mailbox addressThis failure might be caused by the following conditions:

• The recipient's email address was entered incorrectly by the sender.
• No recipient's exists in the destination email system.
The recipient's mailbox has been moved and the Outlook recipient cache on the sender's computer hasn't updated.
• An invalid legacy domain name (DN) exists for the recipient's mailbox Active Directory Domain Service.

This error typically occurs when the sender of the message incorrectly enters the email address of the recipient. The sender should check the recipient's email address and send again. This error can also occur if the recipient email address was correct in the past but has changed or has been removed from the destination email system.

If the sender of the message is in the same organization as the recipient, and the recipient's mailbox still exists, determine whether the recipient's mailbox has been relocated to a new email server. If this is the case, Outlook might not have updated the recipient cache correctly. Instruct the sender to remove the recipient's address from sender's Outlook recipient cache and then create a new message. Resending the original message will result in the same failure.

For more information, see Fix email delivery issues for error code 5.1.1 through 5.1.20 in Exchange Online.

5.1.8Access denied, bad outbound senderThe account has been blocked for sending too much spam. Typically, this problem occurs because the account has been compromised (hacked) by phishing or malware.For more information, see Fix email delivery issues for error code 5.1.8 in Exchange Online.5.1.10Recipient not foundThe recipient's <SMTP Address> wasn't found by SMTP address lookup.For more information, see Fix email delivery issues for error code 550 5.1.10 in Exchange Online.5.1.90Your message can't be sent because you've reached your daily limit for message recipientsThe sender has exceeded the recipient rate limit as described in Sending limits.This could indicate the account has been compromised and is being used to send spam. For more information, see How to determine whether your account has been compromised.5.2.2Submission quota exceededThe sender has exceeded the recipient rate limit or the message rate limit as described in Sending limits.This could indicate the account has been compromised and is being used to send spam. For more information, see How to determine whether your account has been compromised.5.2.121Recipient's per hour message receive limit from specific sender exceeded.The sender has exceeded the maximum number of messages they're allowed to send per hour to a specific recipient in Exchange Online.The automated mailer or sender should try again later, and reduce the number of messages they send per hour to a specific recipient.

This limit helps protect Microsoft 365 or Office 365 users from rapidly filling their inboxes with a large number of messages from errant automated notification systems or other single-sender mail storms.

5.2.122Recipient's per hour message receive limit exceeded.The Microsoft 365 or Office 365 recipient has exceeded the number of messages they can receive per hour from all senders.The automated mailer or sender should try again later, and reduce the number of messages they send per hour to a specific recipient.

This limit helps protect Microsoft 365 and Office 365 users from rapidly filling their inboxes with a large number of messages from errant automated notification systems or other mail storms.

5.3.190Journaling on-premises messages to Microsoft 365 or Office 365 not supported when Journaling Archive is disabled.Journaling on-premises messages to Microsoft 365 or Office 365 isn't supported for this organization because they haven't turned on Journaling Archive in their settings.A journaling rule is configured in the organization's on-premises environment to journal on-premises messages to Microsoft 365 or Office 365, but Journaling Archive is disabled. For this scenario to work, the organization's Office 365 administrator should either enable Journaling Archive or change the journaling rule to journal messages to a different location.5.4.1Relay Access DeniedThe mail server that's generating the error doesn't accept mail for the recipient's domain. This error is caused by mail server or DNS misconfiguration.For more information, see Fix email delivery issues for error code 5.4.1 in Exchange Online.5.4.1Recipient address rejected: Access deniedThe recipient's address doesn't exist.For more information, see Use Directory Based Edge Blocking to reject messages sent to invalid recipients.5.4.6 or 5.4.14Routing loop detectedA configuration error has caused an email loop. 5.4.6 is generated by on-premises Exchange server (you'll see this code in hybrid environments). 5.4.14 is generated by Exchange Online.

By default, after 20 iterations of an email loop, Exchange interrupts the loop and generates an NDR to the sender of the message.

This error occurs when the delivery of a message generates another message in response. That message then generates a third message, and the process is repeated, creating a loop. To help protect against exhausting system resources, Exchange interrupts the mail loop after 20 iterations. Mail loops are typically created because of a configuration error on the sending mail server, the receiving mail server, or both. Check the sender's and the recipient's mailbox rules configuration to determine whether automatic message forwarding is enabled.

For more information, see Fix email delivery issues for error code 5.4.6 or 5.4.14 in Exchange Online.

5.4.300Message expiredThe email took too long to be successfully delivered, either because the destination server never responded or the sent message generated an NDR error and that NDR couldn't be delivered to the original sender.5.5.0550 5.5.0 Requested action not taken: mailbox unavailableThe recipient's <SMTP Address> domain is @hotmail.com or @outlook.com and it wasn't found by SMTP address lookup.Similar to 550 5.1.10. For more information, see Fix email delivery issues for error code 550 5.1.10 in Exchange Online.5.6.11Invalid charactersYour email program added invalid characters (bare line feed characters) into a message you sent.For more information, see Fix email delivery issues for error code 5.6.11 in Exchange Online.5.7.1Delivery not authorizedThe sender of the message isn't allowed to send messages to the recipient.This error occurs when the sender tries to send a message to a recipient but the sender isn't authorized to do this. This frequently occurs when a sender tries to send messages to a distribution group that has been configured to accept messages only from members of that distribution group or other authorized senders. The sender must request permission to send messages to the recipient.

This error can also occur if an Exchange transport rule rejects a message because the message matched conditions that are configured on the transport rule.

For more information, see Fix email delivery issues for error code 5.7.1 in Exchange Online.

5.7.1Unable to relayThe sending email system isn't allowed to send a message to an email system where that email system isn't the final destination of the message.This error occurs when the sending email system tries to send an anonymous message to a receiving email system, and the receiving email system doesn't accept messages for the domain or domains specified in one or more of the recipients. The following are the most common reasons for this error:

• A third party tries to use a receiving email system to send spam, and the receiving email system rejects the attempt. By the nature of spam, the sender's email address might have been forged, and the resulting NDR could have been sent to the unsuspecting sender's email address. It's difficult to avoid this situation.
• An MX record for a domain points to a receiving email system where that domain isn't accepted. The administrator responsible for the specific domain name must correct the MX record or configure the receiving email system to accept messages sent to that domain, or both.
• A sending email system or client that should use the receiving email system to relay messages doesn't have the correct permissions to do this.

For more information, see Fix email delivery issues for error code 5.7.1 in Exchange Online.

5.7.1Client was not authenticatedThe sending email system didn't authenticate with the receiving email system. The receiving email system requires authentication before message submission.This error occurs when the receiving server must be authenticated before message submission, and the sending email system hasn't authenticated with the receiving email system. The sending email system administrator must configure the sending email system to authenticate with the receiving email system for delivery to be successful.

For more information, see Fix email delivery issues for error code 5.7.1 in Exchange Online.

5.7.12Sender was not authenticated by organizationThe sender's message is rejected because the recipient address is set up to reject messages sent from outside of its organization. Only an email admin for the recipient's organization can change this.For more information, see Fix email delivery issues for error code 5.7.12 in Exchange Online.5.7.23The message was rejected because of Sender Policy Framework violationThe destination email system uses SPF to validate inbound mail, and there's a problem with your SPF configuration.For more information, see Fix email delivery issues for error code 5.7.23 in Exchange Online.5.7.57Client was not authenticated to send anonymous mail during MAIL FROMYou configured an application or device to send (relay) email messages in Microsoft 365 or Office 365 using the smtp.office365.com endpoint, and there's a problem with the configuration of the application or device.For more information, see Fix email delivery issues for error code 5.7.57 in Exchange Online.5.7.64TenantAttribution; Relay Access DeniedYou use an inbound connector to receive messages from your on-premises email environment, and something has changed in your on-premises environment that makes the inbound connector's configuration incorrect.For more information, see Fix email delivery issues for error code 5.7.64 in Exchange Online.5.7.124Sender not in allowed-senders listThe sender doesn't have permission to send to the distribution group because the sender isn't in the group's allowed-senders list. Depending how the group is set up, even the group's owner might need to be added to the allowed sender list in order to send messages to the group.For more information, see Fix email delivery issues for error code 5.7.124 in Exchange Online.5.7.133Sender not authenticated for groupThe recipient address is a group distribution list that is set up to reject messages sent from outside of its organization. Only an email admin for the recipient's organization or the group owner can change this.For more information, see Fix email delivery issues for error code 5.7.133 in Exchange Online.5.7.134Sender was not authenticated for mailboxThe recipient address is a mailbox that is set up to reject messages sent from outside of its organization. Only an email admin for the recipient's organization can change this.For more information, see Fix email delivery issues for error code 5.7.134 in Exchange Online.5.7.13 or 135Sender was not authenticated for public folderThe recipient address is a public folder that is set up to reject messages sent from outside of its organization. Only an email admin for the recipient's organization can change this.For more information, see Fix email delivery issues for error code 5.7.13 or 5.7.135 in Exchange Online.5.7.136Sender was not authenticatedThe recipient address is a mail user that is set up to reject messages sent from outside of its organization. Only an email admin for the recipient's organization can change this.For more information, see Fix email delivery issues for error code 5.7.136 in Exchange Online.5.7.25Access denied, the sending IPv6 address [2a01:111:f200:2004::240] must have a reverse DNS recordThe sending IPv6 address must have a reverse DNS record in order to send email over IPv6.For more information, see Support for anonymous inbound email messages over IPv6.5.7.321starttls-not-supported: Destination mail server must support TLS to receive mail.

• DNSSEC checks have passed, yet upon connection the destination mail server doesn't respond to the STARTTLS command.
• The destination server responds to the STARTTLS command, but the TLS handshake fails.

This message usually indicates an issue on the destination mail server. Check the validity of the recipient address and determine if the destination server is configured correctly to receive messages.5.7.322certificate-expired: Destination mail server's certificate is expired.DNSSEC checks have passed, yet upon establishing the connection the destination mail server provides a certificate that is expired.A valid X.509 certificate that isn't expired must be presented. X.509 certificates must be renewed after their expiration, commonly annually.5.7.323tlsa-invalid: The domain failed DANE validation.Records are DNSSEC authentic but one or multiple of these things occurred:

• The destination mail server's certificate doesn't match with what is expected per the authentic TLSA record.
• Authentic TLSA record is misconfigured.
• Destination domain is being attacked.
• The certificate start date is in the future.
• Any other DANE failure.

This message usually indicates an issue on the destination mail server. Check the validity of the recipient address and determine if the destination server is configured correctly to receive messages.

For more information about DANE, see: https://datatracker.ietf.org/doc/html/rfc7671.|

5.7.324 dnssec-invalid: Destination domain returned invalid DNSSEC recordsThe destination domain indicated it was DNSSEC-authentic but Exchange Online wasn't able to verify it as DNSSEC-authentic.For more information about DNSSEC, see: Overview of DNSSEC.5.7.325certificate-host-mismatch: Remote certificate MUST have a common name or subject alternative name matching the hostname (DANE)This happens when the presented certificate identities (CN and SAN) of a destination SMTP target host don't match any of the domains or MX host.This message usually indicates an issue on the destination email server. Check the validity of recipient address and determine if the destination server is configured correctly to receive messages. For more information, see How SMTP DNS-based Authentication of Named Entities (DANE) works to secure email communications.5.7.501Access denied, spam abuse detectedThe sending account has been banned due to detected spam activity.For details, see Fix email delivery issues for error code 451 5.7.500-699 (ASxxx) in Exchange Online.

Verify that any account issues have been resolved, and reset its credentials. To restore this account's ability to send mail, contact support through your regular channel.

5.7.502Access denied, banned senderThe sending account has been banned due to detected spam activity.Verify that any account issues have been resolved, and reset its credentials. To restore this account's ability to send mail, please contact support through your regular channel.5.7.503Access denied, banned senderThe sending account has been banned due to detected spam activity.Verify that any account issues have been resolved, and reset its credentials. To restore this account's ability to send mail, please contact support through your regular channel.5.7.504[email@contoso.com]: Recipient address rejected: Access deniedThe recipient address that you're attempting to contact isn't valid.Verify the recipient's email address, and try again.5.7.505Access denied, banned recipientThe recipient that you're attempting to contact isn't valid.If you feel this is in error, contact support.5.7.506Access Denied, Bad HELOYour server is attempting to introduce itself (HELO according to RFC 821) as the server it's trying to connect to, rather than its own fully qualified domain name.This isn't allowed, and it's characteristic of typical spambot behavior.5.7.507Access denied, rejected by recipientThe IP that you're attempting to send from has been blocked by the recipient's organization.Contact the recipient in order to resolve this issue.5.7.508Access denied, [$SenderIPAddress] has exceeded permitted limits within $range rangeThe sender's IPv6 range has attempted to send too many messages in too short a time period.Not applicable5.7.509Access denied, sending domain [$SenderDomain] does not pass DMARC verificationThe sender's domain in the 5322.From address doesn't pass DMARC.Not applicable5.7.510Access denied, [contoso.com] does not accept email over IPv6The sender is attempting to transmit a message to the recipient over IPv6, but the recipient doesn't accept email messages over IPv6.Not applicable5.7.511Access denied, banned senderThe IP that you're attempting to send from has been banned.To delist the address, email delist@messaging.microsoft.com and provide the full NDR code and IP address to delist.

For more information, see Use the delist portal to remove yourself from the blocked senders list.

5.7.512Access denied, message must be RFC 5322 section 3.6.2 compliantMessage was sent without a valid "From" email address.Office 365 only. Each message must contain a valid email address in the "From" header field. Proper formatting of this address includes angle brackets around the email address, for example, <security@contoso.com>. Without this address Microsoft 365 or Office 365 will reject the message.5.7.513Service unavailable, Client host [$ConnectingIP] blocked by $recipientDomain using Customer Block list (AS16012607)The recipient domain has added your sending IP address to its custom blocklist.The domain that received the email has blocked your sender's IP address. If you think your IP address has been added to the recipient domain's custom blocklist in error, you need to contact them directly and ask them to remove it from the blocklist.5.7.606-649Access denied, banned sending IP [IP1.IP2.IP3.IP4]The IP that you're attempting to send from has been banned.Verify that you're following the best practices for email deliverability, and ensure your IPs' reputations haven't been degraded as a result of compromise or malicious traffic. If you believe you're receiving this message in error, you can use the self-service portal to request to be removed from this list.

For more information, see Use the delist portal to remove yourself from the blocked senders list.

5.7.703Your message can't be delivered because one or more recipients are blocked by your organization's tenant recipient block policySomeone in your organization sent mail to an email address or domain that's blocked in the Tenant Allow/Block List. The entire message is blocked for all recipients of the message, even if only one recipient email address or domain is defined in a block entry.5.7.705

5.7.708

5.7.705 Access denied, tenant has exceeded threshold, 5.7.708 Access denied, traffic not accepted from this IPThe majority of traffic from this tenant has been detected as suspicious and has resulted in a ban on sending ability for the tenant.Ensure that any compromises or open relays have been resolved, and then contact support through your regular channel.

For more information, see Fix email delivery issues for error codes 5.7.700 through 5.7.750 in Exchange Online.

5.7.750Service unavailable. Client blocked from sending from unregistered domainsA suspicious number of messages from unprovisioned domains is coming from this tenant.Add and validate any and all domains that you use to send email from Microsoft 365 or Office 365.

For more information, see Fix email delivery issues for error codes 5.7.700 through 5.7.750 in Exchange Online.

n/aThe message can't be submitted because the sender's submission quota was exceededThe user account has exceeded the recipient rate limit (10,000 recipients per day).The account has likely been compromised. For more information, see Fix email delivery issues for error 'the sender's submission quota was exceeded' in Exchange Online.