Outlook issue

Question

We are currently facing an issue with Microsoft Outlook. Inbox emails are appearing in Conversation History, and emails are not being delivered to the respective recipients. The system is showing delivery failures, and in some cases, emails are automatically being sent or re-sent to parties without proper delivery confirmation.

Answer 1

Hi @Admin Maverick Law, 

I hope you’re doing well. Thank you for reaching out and I appreciate you sharing the details of what you’re experiencing in Microsoft Outlook. 

Before we proceed, please note that this is a user-to-user community forum. As a moderator, I don’t have access to your Microsoft 365 tenant, your account, or your device to make changes directly. However, I’ll do my best to support you by sharing the appropriate resources and directing you to the right support channels. 

From your description, there are two main symptoms happening: 

First, emails showing up in Conversation History is not typical default behavior in Outlook. This is often caused by an Outlook rule, an add-in, or a filtering/view setting that is moving/copying messages. 

Second, delivery failures and “automatic re-sending” generally point to mail flow interruptions (server-side) or client re-try behavior (Outlook attempting to resend when it thinks a send did not complete successfully commonly due to sync/cache issues or connection interruptions). 

Here are some steps you can try to address this: 

1/ Check rules that may be moving emails 

1. In Outlook, please go to File > Manage Rules & Alerts 
2. Under Email Rules, review rules for anything that moves/copies to “Conversation History” 
3. Temporarily disable suspicious rules, then test again. 

If possible, also check rules via Outlook on the web (OWA), as some rules may be server-side. 

2/ Test whether an add-in is causing the behavior 

1. Close Outlook 
2. Start Outlook in Safe Mode: 
3. Windows + R > type: outlook.exe /safe > Enter 
4. 
5. Observe if emails still appear in Conversation History and if sending still fails. 

If the issue stops in Safe Mode: 

• Go to File > Options > Add-ins > COM Add-ins > Go… 
• 
• Disable add-ins (especially antivirus, CRM, archiving, signature/encryption tools) and re-enable one-by-one to identify the cause. 

3/ Reduce duplicate sends / resend behavior  

1. Check Outbox for stuck items 
2. Try Send/Receive once (avoid repeated clicking) 
3. Toggle Offline/Online: Send/Receive > Work Offline (wait 10 seconds) > turn it off 
4. 
5. Restart Outlook and test sending a small email to a single recipient. 

If duplicates continue, we may need to refresh the local cache (OST) or profile (see option 5). 

4/ Verify if this is Outlook-only or server-side 

Please try sending the same email using Outlook on the web (OWA): 

• If it works in OWA but fails in Classic Outlook > likely a client/cache/profile/add-in issue 
• Otherwise, if it fails in OWA as well > likely mail flow / policy / server-side (Exchange) issue 

5/ If needed, reset the Outlook profile 

If the issue persists after steps above, I recommend creating a fresh Outlook profile: 

• Close Outlook  
• Open Control Panel > Mail (Microsoft Outlook) > Show Profiles  
• Click Add… to create a new profile  
• Add your email account and open Outlook using the new profile  
• Re-test sending/receiving 

Please understand that our initial reply may not always immediately resolve the issue. However, with your help and more detailed information, we can work together to find a solution.   

I hope this information is helpful. Should you have any further questions or need additional assistance, please feel free to share them in the comment below. I'm very happy to help you with the next steps.

Thank you again for your understanding and cooperation. 

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Answer 2

Based on the described symptoms, focus on two main areas: rules/redirects that are misfiling mail, and delivery/NDR issues that may be client- or mailbox-related.

1. Check for hidden or unexpected rules and forwarding Inbox items appearing in Conversation History and messages auto‑sending or re‑sending strongly suggests a rule or forwarding configuration is diverting or reprocessing mail.

In Outlook on the web for the affected mailbox(es):

1. Open the mailbox in a browser and go to Settings → Mail → Rules.
2. Look for any rules that:
   • Move all or most incoming mail to Conversation History, RSS Feeds, or other folders.
   • Forward, redirect, or auto‑reply to external addresses.
3. Disable or delete any unrecognized or overly broad rules and test again.

Also check:

• Settings → Mail → Forwarding to ensure there is no unexpected forwarding configured.

A similar case was resolved by removing a hidden rule that diverted all new mail to RSS Feeds, which stopped normal delivery.

2. Review NDRs and delivery failure details For messages that are not being delivered and generate NDRs or postmaster messages:
3. Open the NDR and scroll to Diagnostic information for administrators.
4. Note the error text and codes (for example, 0x80040305, 0x80004005, or SMTP errors like 554 5.2.0 or “Mailbox not found”, “Mailbox full”, “Message too large”, etc.).
5. Act based on the specific reason:
   • Invalid/unknown mailbox or domain: Verify the recipient address and domain spelling and that the mailbox still exists.
   • Mailbox full / quota exceeded: Ask the recipient to clear space.
   • Message too large: Reduce attachment size or use OneDrive for file sharing.
   • Temporary server issues (connection timed out, no adequate servers, resources temporarily unavailable): Wait and resend later.

If the NDR is from ******@outlook.com, postmaster@microsoft.com, or service.microsoft.com, treat it as a legitimate delivery failure notification and use the diagnostic section to determine the cause.

3. Check for Outlook client bugs or sync issues If Outlook is generating NDRs with specific error codes or messages, compare with known issues:

• If NDRs contain error 0x80040305 and mention Submit-Message failed with that HResult, ensure Outlook is updated to a build that includes the fix for this issue. Updating Outlook for Microsoft 365 to the latest version resolves this specific NDR scenario.
• If emails are stuck in Outbox or undeliverable and the Sync Issues folder shows errors like 80040611 or NDRs mention StoragePermanentException: Invalid named property, this can indicate a mailbox property quota issue (often triggered by certain add‑ins like Digital Guardian). In that case:
  1. Temporarily pause or disable the implicated add‑in/security product on affected machines.
  2. Open a support case from the Microsoft 365 Admin Portal and request a mailbox move as mitigation.
  3. After the mailbox move completes, recreate the Outlook profile/OST for the user.

4. Validate that the issue is not client‑specific To distinguish between Outlook‑client issues and mailbox/server issues:
5. Have an affected user sign into Outlook on the web and test sending/receiving.
   • If mail flows correctly in the browser but not in the desktop client, focus on the Outlook profile, add‑ins, and local rules.
   • If the same behavior occurs in the browser, the problem is at the mailbox or service level (rules, forwarding, quota, or server‑side issues).
6. Next steps if issues persist If:

• No unexpected rules/forwarding are present,
• NDRs do not match the documented issues above, and
• The problem reproduces in Outlook on the web,

then open a support case from the Microsoft 365 Admin Center, attach sample NDRs (with full headers and diagnostic sections), and reference the relevant Outlook delivery and sync articles so support can check for mailbox corruption, property quota issues, or service‑side problems.

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References:

• Outlook sync issues cause emails to be stuck in the Outbox and undeliverable mail items
• Emails sent using Outlook Desktop results in Non-Delivery Report [0x80040305-0x00000000-0x00000000]
• Outlook replies or forwards cause non-delivery error “Your message did not reach some or all of the intended recipients”
• Sent email in Outlook.com comes back "delivery failed"
• Failed delivery messages from the postmaster at outlook.com, microsoft.com, or service.microsoft.com
• Stopped receiving emails on my account. - Microsoft Q&A
• my outlook email is not delivered - Microsoft Q&A
• - ******@yahoo.com Sorry, we were unable to deliver your message - Microsoft Q&A