Email not delivered but the address is correct: Causes and solutions in Outlook

When we meet a Email not delivered in OutlookThe first thing we think is that it was our mistake. However, sometimes we are astonished to discover that the address is correct. What happened?

The causes can be varied: mailbox limits, spam filters, temporary server issues, or even local rules and configurations. There is almost always a locatable explanation and a concrete remedy.. we review all this below.

Undelivered Email in Outlook: Quick Checks

In many cases, The non-delivery notice shares the same cause as the classic mailbox not found notice.: a temporary issue with the recipient's account or server. Before trying the full range of solutions, it's worth trying a few:

• Wait a few minutes and resend the messageSometimes it's just a matter of trying again.
• Double-check the recipient's address and contact them by another means. to confirm whether you are using a new address.
• Confirm that Outlook is not working offlineIn the status bar, if you see Offline, Working Offline, or the message "Trying to connect," turn on online mode: Send/Receive tab, Preferences group, Work Offline option to toggle. You may need to open the message and forward it, or tap Send/Receive.
• check your accountIf you changed your password, update it on all devices. If unusual activity was detected, your account may be temporarily locked.

Outlook on the Web and Problem Support Assistant in a single user

Usa outlook on the web to isolate whether the mailbox is working correctly on the serverIf email is coming in there, the problem is usually with your profile, Outlook version, or add-ins on your PC.

Run the Microsoft Support and Recovery Assistant (SaRA) on the affected computer. This detects common Outlook and Microsoft 365 issues (licenses, profile, version, configuration) and guides you through fixes. If the issue is Outlook for Mac or mobile access, You can check the settings with the app, but installing the wizard requires a PC.

 

Microsoft 365 Tools for Administrators

Microsoft 365 It has a number of useful tools for the problem of undelivered email in Outlook when the address is correct:

• Microsoft 365 Service StatusIn the Admin Center, under Service Status, check if Exchange Online shows any degradation or issues. If there are issues, delivery may be delayed, and engineers are already working.
• Mail Delivery TroubleshooterIn the Admin Center, run Diagnostics. Troubleshoot email delivery issues. Enter the sender and recipient addresses and run the tests to find suggested causes and fixes.
• Message tracking in the Exchange admin center. Allows you to track a message as it travels through Exchange Online to answer user questions, debug mail flow, or validate policy changes. How to open it if you're an administrator: Sign in to Microsoft 365, select Admin, go to Exchange, and under Mail Flow, select Message Tracking.
• Run a follow-up limited to the relevant user and period. By default it searches for 48 hours. Set Date Range, add sender and recipient and press SearchIn the results you will see the status (for example, Delivered). Select a message to view Details and follow the Correction prompts. For another search, use Clear and redefine criteria.

Follow-up FAQsData may take 10 minutes to an hour to appear; if you see a timeout error, simplify the criteria. If a message takes a long time, the causes include an unresponsive destination, very long messages, service latency, or blocking filters.

Outlook.com: When you can't send

Sometimes the cause of an undelivered email in Outlook is try to attach files larger than 25 MBThe solution for these cases is to reduce or share via the cloud.

Other possibilities are:

• Dnon-existent recipient address.
• Recipient's mailbox full.
• Server problems of destiny.
• Antispam filters that mark your message as spam.

If you use a signature, try removing it if it gives an error. and forward. Ask the recipient to add you to their safe senders list and make sure you've saved the contact to your address book. If you see an error connecting to the recipient's server, update your address or alias from your Outlook.com settings.

 

If you schedule a message with "Do not deliver before" and is not sent at the scheduled time, it is usually due to Cached Exchange Mode because Outlook wasn't open at the time. In cached mode, Outlook uses a local .ost file and places the message in the local Outbox. The server can't send it without Outlook running to synchronize.

If you see states like Offline or Working Offline, return to online mode as described above and retry sending. If the message is still in your Outbox, open it, check the scheduled time, and send it again.

NDR codes and typical causes in Exchange Online and Outlook

The NDR notices These are very useful in Outlook email undeliverable situations. They include numeric codes that indicate the cause of the error (which helps us find an appropriate solution). Below is a summary of 4.xx and 5.xx codes, along with their meaning and most common actions:

• 432 4.3.2 STOREDRV.Deliver; container thread limit exceeded: The recipient's mailbox is limiting reception because too much mail is arriving too quickly; this is a database protection measure. Please wait and try again.
• 4.4.7 Message expired: The queued message has expired after failed attempts. This is usually due to a problem with the receiving server, timeouts, or header limits. Check the destination server's address and configuration; reduce recipients if necessary and resend.
• 4.4.8 MX hosts of domain failed MTA-STS validation: The destination MX host does not match the domain's MTA-STS policy. Review the destination domain's policy.
• 4.4.316 Connection refused : Unable to connect to the external server; this is almost always a problem with the recipient or their network. Use the message's IP address to identify the responsible party.
• 450 4.4.317 Cannot connect to remote server : The full certificate chain is missing during the TLS handshake; Exchange Online cannot validate. Adjust certificates on the remote server.
• 4.5.3 Too many recipients: More than 200 SMTP envelope recipients from the same domain. Divide the sending into smaller batches.
• 4.7.5 Remote certificate failed MTA-STS validation: Target server certificate does not chain to a trusted CA or names do not match STS policy.
• 4.7.26 Access denied, message sent via IPv6 must pass SPF or DKIM: absent signature. Configure SPF or DKIM for IPv6.
• 4.7.321 starttls-not-supported: After passing DNSSEC, the server doesn't respond correctly to STARTTLS or the handshake fails. Check the destination server's configuration.
• 4.7.322 certificate-expired: The destination server certificate has expired; please renew the X.509.
• 4.7.323 tlsa-invalidDANE validation failed; TLSA mismatch, misconfigured, or under attack. Check DANE and TLSA.
• 4.7.324 dnssec-invalid: The destination indicates DNSSEC but cannot be validated as authentic. Check DNSSEC.
• 4.7.325 certificate-host-mismatch: The certificate's CN or SAN doesn't match the domain or MX host. Adjust the certificate or MX according to DANE.
• 4.7.500-699 Access denied: suspicious activity detected; temporary restriction while evaluating.
• 4.7.850-899 Access denied: suspicious activity on the IP; temporary blocking.
• 5.0.350 generic error such as x-dg-ref header is too long or Requested action not taken: policy violation detected (AS345). Check RTF format and nested attachments.
• 5.1.0 Sender denied: Incorrectly formatted or unresolvable recipient address; common when replying to .msg files saved with legacyExchangeDN. Correct the address and resend.
• 5.1.1 Bad destination mailbox address: Misspelled or missing recipient email, outdated recipient cache, or invalid legacy DN. Clear the AutoComplete cache and propagate a new message.
• 5.1.8 Access denied, bad outbound sender: Account blocked for sending spam; usually compromised. Reset credentials and clean up devices.
• 5.1.10 Recipient not found: The recipient's SMTP address cannot be found; please validate and correct it.
• 5.1.20 Multiple From without Sender: Multiple addresses in From without specifying Sender. Adjusts headers according to RFC.
• 5.1.90 daily recipient limit reached: exceeds sending limits; may indicate compromise.
• 5.2.2 Submission quota exceeded: : Recipient or message frequency limit exceeded.
• 5.2.121 Recipient hourly limit from a sender exceeded: reduces the hourly rate towards that recipient.
• 5.2.122 hourly reception limit exceeded: the recipient has reached its time limit.
• 5.3.190 On-premises journaling to Microsoft 365 is not supported if journal archiving is disabled: Enables journaling or changes the journaling destination.
• 5.4.1 Relay Access Denied: The server is not accepting mail for the domain; server or DNS configuration error.
• 5.4.1 Recipient address rejected: Access denied: Non-existent recipient; uses directory-based edge blocking to reject invalid recipients.
• 5.4.6 or 5.4.14 Routing loop detected: Mail loop by configuration. Check automatic forwarding and rules at the source and destination.
• 5.4.8 MX hosts failed MTA-STS validation: The MX host does not match the domain's STS policy.
• 5.4.300 Message expired: The email took too long or the NDR could not be returned to the sender.
• 5.5.0 550 5.5.0 Requested action not taken: mailbox unavailable: hotmail.com or outlook.com domains not found in SMTP search; similar to 5.1.10.
• 5.6.11 Invalid characters: The client added invalid full-line font characters; please correct the formatting.
• 5.7.1 Delivery not authorized: Sender not authorized to send to that recipient or group. Request permission or adjust transport rules.
• 5.7.1 Unable to relay: The sending system is attempting an unauthorized relay, or the recipient doesn't accept the specified domains. This is also typical in spam attempts. Adjust MX or relay permissions.
• 5.7.1 Client was not authenticated: The receiving server requires authentication before sending; configure authentication.
• 5.7.5 Remote certificate failed MTA-STS: : Problem with destination server certificate according to MTA-STS.
• 5.7.12 Sender was not authenticated by organization: The recipient rejects external emails; only an admin can change this.
• 5.7.23 SPF violation: SPF failure according to the destination domain policy.
• 5.7.25 IPv6 without Reverse DNS: The sending IPv6 address requires PTR.
• 5.7.57 Client not authenticated to send anonymously during MAIL FROM: Misconfigured devices or apps against smtp.office365.com.
• 5.7.64 TenantAttribution; Relay Access Denied: Input connector misaligned after on-premises changes.
• 5.7.124 Sender not in allowed-senders list: Sender is not on the distribution group's allowed list.
• 5.7.133 Sender not authenticated for group: Group set to reject outsiders; adjust permissions or ask the owner.
• 5.7.134 Sender was not authenticated for mailbox: mailbox set to reject external.
• 5.7.13 or 5.7.135 Sender was not authenticated for public folder: : public folder blocks externals.
• 5.7.136 Sender was not authenticated for mail user: : mail user rejects external.
• 5.7.232 Test tenant exceeded the limit of external recipients in 24 hours: Sending to external parties is blocked until it falls below the threshold.
• 5.7.233 Tenant exceeded the limit of external recipients: gradual control in a 24-hour window.
• 5.7.321 starttls-not-supported: STARTTLS not supported or handshake failed after DNSSEC.
• 5.7.322 certificate-expired: Certificate expired on the destination server.
• 5.7.323 tlsa-invalid: DANE validation fails due to multiple possible causes (including future start date).
• 5.7.324 dnssec-invalid: Invalid DNSSEC records returned by the target domain.
• 5.7.325 certificate-host-mismatch: CN or SAN does not match MX domain or host according to DANE.

NDR warnings include numerical codes that indicate the cause of the failure.. Then, A compendium of 4.xx and 5.xx codes with their meaning and actions more common:

Delivery and read receipts: how they work and how to activate them

The delivery confirmations Read receipts prove that the message arrived in the mailbox, and that it was opened. An important detail: the recipient can refuse to send read receipts, and some clients don't support them. That is, you can't force anyone to send them.

• New Outlook on Windows: When composing, select the Options tab and under Tracking, select Request a Delivery Receipt or Request a Read Receipt. If you don't see the option, open More Options on the far right of the ribbon and select it.
• Classic Outlook on WindowsIn a new email, go to the Options tab > Tracking, select the confirmation box you need, and send. If you're composing in the Reading Pane, go to the Message tab > Labels group > open Properties and choose the appropriate voting and tracking options.
• outlook on the web: When composing, Options tab > Tracking, aActivate delivery or read receipts. If they don't appear in Options, use More Options at the end of the ribbon.
• Outlook.comYou can't request read receipts directly on the Outlook.com web, but you can request them when sending from Outlook for Windows using an Outlook.com account. In Outlook.com, you can choose how to respond to read requests in Settings > Read Receipts.

Every non-delivery issue has a helpful hint in the NDR or Microsoft 365 tools.; with an organized review of Outlook's address, service status, diagnostics, message tracking, anti-spam policies, limits, and local settings. a reliable and predictable mail flow can be reestablished.