outlook.com sends messages to Sent Items but recipients never receive them

Carlton Johnson PhD 5 Reputation points
2026-10-14T13:25:48.55+00:00

I'm using a personal Outlook account in a web browser. Messages appear in Sent Items with no error or bounce back but recipients do not receive them, including Gmail addresses. Incoming email works normally. My mailbox is only 26% full. I've tested multiple recipients, checked spam, outbox, drafts, forwarding, and rules. Service status shows Outlook operational and the Microsoft Sign-in Helper reports no problems with my account. How can I resolve this apparent outbound delivery issue?

Outlook | Web | Outlook.com | Email
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  1. AI answer

    2026-10-14T13:26:05.4666667+00:00

    Since the issue occurs in Outlook.com in a browser, incoming mail works, storage is not full, and messages go to Sent Items with no NDR, focus on outbound delivery checks that match silent send failures:

    1. Send a new plain test message from Outlook.com
      • Remove any signature.
      • Do not include attachments.
      • Send to a Gmail address and another external address.
      • This helps rule out signature-related send problems and message-size issues.
    2. Check attachment size on any failing messages
      • Outlook.com cannot send a message with an attachment larger than 25 MB.
      • If the original message is large, upload the file to OneDrive and send a link instead.
    3. Verify recipient addressing carefully
      • If any recipient address is invalid, changed, or misspelled, mail can fail or be undeliverable.
      • Re-enter the full address manually instead of relying on saved entries.
    4. Try sending from Outlook.com specifically for comparison
      • For undeliverable scenarios when using another mail app, Microsoft recommends trying Outlook.com directly. In this case, that already confirms the problem is account-side or delivery-side rather than a local app issue.
    5. Consider recipient-side filtering or blocking
      • When mail shows as sent but no NDR is returned, recipient-side filtering is a common cause.
      • Ask recipients to check spam, quarantine, and any mail filtering on their side.
      • If the recipient is on a managed or enterprise mail system, ask their mail administrator to run a message trace and check whether the message was blocked, quarantined, or redirected.
    6. Check whether the sending account is under a temporary sending restriction
      • Outlook.com can apply a temporary low sending quota to newer accounts until credibility is established.
      • If the account is relatively new, review sending limits.
    7. If a non-delivery receipt appears later, use the exact error text to match the fix
      • blocked / listed in / spamhaus / spamcop / blackhole / dynablock: the recipient server is blocking the sending server or account; the recipient’s provider must unblock it.
      • mailbox full / quota exceeded: the recipient must free mailbox space.
      • host unknown / domain lookup failed / mailbox not found / user unknown: verify the address and confirm the recipient still uses that mailbox.
      • undeliverable: reduce recipients and confirm the address is valid.
    8. If all recipients, including Gmail, still do not receive plain test messages from Outlook.com
      • Use Outlook.com support options from the Help menu or the Outlook.com support entry point.
      • At that stage, the evidence points to an Outlook.com outbound delivery issue or account restriction rather than browser settings, mailbox capacity, rules, forwarding, or sign-in problems.
    AI-generated content may be incorrect. Read our transparency notes for more information.

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  2. Hornblower409 17,065 Reputation points
    2026-10-15T01:42:52.9533333+00:00

    @Carlton Johnson PhD said

    Outlook account in a web browser. Messages appear in Sent Items with no error or bounce back but recipients do not receive them, including Gmail addresses. Incoming email works normally

    If the AI Answer did not solve your issue, could I get some additional details please:

    Can you send/receive to yourself at the same Outlook.com address?

    Can you send to another Outlook.com/Hotmail account?

    Does the problem occur if you use a Private/Incognito browser window to access Outlook Web?

    Did sending previously work and, if so, when did it stop?

    Do you have any other Outlook Clients you could test with? e.g. New Outlook for Windows, Outlook Mobile?

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