If your email isn’t being delivered, first work out whether it is stuck in your Outbox, rejected with a nondelivery report, delayed, or delivered somewhere other than the Inbox. Check your connection and mailbox, then use any bounce code or provider trace to identify what happened. DNS authentication fixes are for the person who manages the sending domain—not usually an individual mailbox user.
Identify what “not delivered” means
“Sent” in your email app does not necessarily mean that a message reached the recipient’s Inbox. It may still be queued in your Outbox, rejected by the recipient’s mail system, delayed, or filtered into Junk or quarantine.
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Before changing settings, note whether the problem affects one message or all messages, and one recipient or many. Record the sender, recipient, subject, and approximate send time. If appropriate, send a brief test to an address you know is working; avoid sending sensitive information just to test delivery.
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- You received a bounce or nondelivery report (NDR): preserve the entire notice and use its error code and diagnostic text.
- No bounce, but the recipient cannot find the message: check Junk, quarantine, rules, and administrator-side mail tracing.
- Several recipients at different providers are affected: a sender-domain or sending-service issue may be involved, but confirm it from the error details rather than assuming.
Check your email app and mailbox
If you use Outlook, begin with Internet access, then inspect the Outbox and confirm that the account is connected and its credentials are current. Check available mailbox storage as well: a full Microsoft cloud mailbox can prevent sending and receiving. Microsoft’s troubleshooting steps vary by New Outlook, classic Outlook, and third-party accounts, so follow the instructions for your version.
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For other mail apps, look for the equivalent connection and account-status indicators. If a message is stuck, try reconnecting, then send a short new message after confirming the account is online. Avoid repeatedly resending a message that may already have gone out; check Sent first.
Microsoft’s Outlook sending and receiving troubleshooting guide covers common connection, Outbox, and mailbox problems.
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Use a bounce message to find the reason
A nondelivery report is useful evidence, not just a generic failure alert. Microsoft says Exchange Online NDRs typically include an error code and technical details that help explain why delivery failed. Read the full report, check the recipient address for a typo, and follow the instructions tied to the code. Causes can include an invalid address or a recipient-side policy rejection.
A message from a postmaster address usually indicates a delivery failure, but sender names and addresses can be spoofed. Microsoft advises checking that the notice genuinely came from a postmaster address before trusting links or attachments in it.
For an Exchange Online delivery failure, use the code and explanation in Microsoft’s NDR and SMTP error guide. The same code should not be treated as a universal diagnosis across all email providers; the receiving provider’s own explanation matters.
Check whether the message went to Junk or quarantine
If the recipient sees no bounce, ask them to check Junk or Spam, quarantine if available, and any inbox rules that might move or delete messages. In Exchange Online, administrators can use message trace to investigate nonreceipt, delays, spam, malware, and mail-flow rules or policies. A trace marked Delivered does not by itself prove the message landed in the Inbox: Exchange Online may classify it as spam and send it to Junk or quarantine while retaining that status.
If you are the recipient, check the folders and ask your organization’s mail administrator to investigate. If you are the sender, the recipient’s administrator may need to check the trace or quarantine. See Microsoft’s Exchange Online message trace FAQ.
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When sender-domain authentication may be involved
SPF, DKIM, and DMARC are domain-level email authentication mechanisms. They are relevant when you manage the sending domain or can ask its administrator to investigate; they are not settings an ordinary Outlook or Gmail user should edit. An administrator should examine the affected message’s Authentication-Results header and the domain’s DNS and sending configuration.
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nonewhen no SPF record is present,permerrorwhen multiple SPF records exist or the DNS lookup limit is exceeded, andfailorsoftfailwhen the sending IP is not included. Microsoft describes a 10-DNS-lookup limit as a configuration rule, not a statistic about email delivery. - DKIM: a signature can fail if signing or DNS records are incorrect. A gateway that changes a message in transit can also invalidate its signature.
- DMARC: the message needs an aligned SPF or DKIM pass to satisfy DMARC.
Microsoft’s documented examples include NDR 550 5.7.23 for missing or misconfigured SPF and 550 5.7.1 for an unauthorized message; possible causes for the latter include SPF, connectors, or recipient policy. These codes are context-specific, so administrators should use the receiving provider’s full diagnostic rather than infer a cause from the number alone. SPF passing also does not guarantee that a message will avoid spam filtering or reach the Inbox. See Microsoft’s SPF, DKIM, and DMARC troubleshooting guidance.
For Gmail-related sending errors
If Gmail or a Gmail recipient is involved, match the exact SMTP response to Google’s guidance rather than guessing from a generic “failed” notice. Google provides a sender troubleshooting guide and Gmail SMTP error-code explanations.
Administrators of authenticated organization senders can also consult Google Postmaster Tools for aggregate delivery-error information. Google notes that low outgoing volume can leave some daily dashboard data incomplete. It is a sender-side diagnostic, not a personal mailbox setting. See Google Postmaster Tools.
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Choose the next step by the evidence
| What you see | Likely area to investigate | Who can act |
|---|---|---|
| Message stays in Outbox or the account is offline | Connectivity, account status, client sync, or mailbox storage | Usually the account holder |
| NDR names an address or recipient policy problem | Recipient address and the rejection details in the bounce | Sender, or recipient’s administrator for policy restrictions |
| Authentication results show SPF, DKIM, or DMARC problems | DNS records, signing, alignment, and authorized sending systems | Sending-domain administrator |
| No bounce; message is traced as delivered but not in Inbox | Junk, quarantine, recipient rules, or filtering | Recipient and, where needed, mail administrator |
When asking for help, share the provider, approximate send time, error code, and relevant redacted headers with the administrator. Do not post message contents, passwords, or private recipient information publicly.
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