My email account says mail sent but isn't.

Test the affected account in Outlook on the web first: if the same message sends successfully there, repair Classic Outlook; if it also fails there, investigate account-level delivery or recipient filtering.

1. Separate an Outlook application problem from a delivery problem

1. Sign in to the affected account through its provider’s webmail—use Outlook on the web if it is an Outlook.com/Microsoft account.
2. Send a new, attachment-free message to the other account.
3. Check the result:
   • Received: the mailbox can send, so the problem is in Classic Outlook’s profile, synchronization, or add-ins.
   • Not received: the issue is beyond the desktop application. Check the recipient’s Junk, quarantine, forwarding, and rules. A message appearing in Sent Items does not by itself prove delivery to the recipient.

There is no matching sending/delivery incident listed on Microsoft’s current Classic Outlook known-issues page ^1^.

2. If webmail works, diagnose Classic Outlook

1. Look at the bottom status bar. If it says Working Offline, Disconnected, or Trying to connect, select Send/Receive → Work Offline to restore online mode, and then select Send/Receive All Folders.
2. Open Outbox. If an older message is stuck there—especially one with a large attachment—remove the attachment or delete the message, then test again. A large blocked message can prevent later messages from sending ^2^.
3. Run Outlook without add-ins:
   • Close Outlook.
   • Press Windows+R.
   • Enter outlook.exe /safe and press Enter.
   • Send another test message.
   If sending works in Safe Mode, disable—not remove—add-ins under File → Options → Add-ins → Manage: COM Add-ins → Go. Re-enable them individually, restarting Outlook after each one, to identify the problem add-in ^3^.
4. Run Microsoft’s connectivity diagnostic:
   • Open Windows Get Help on the same Windows 10-or-later PC.
   • Run the Classic Outlook connectivity troubleshooter.
   • If it finds nothing, run Classic Outlook advanced diagnostics and retain the resulting configuration report ^4^.

3. Conditional fix for an Outlook.com account paired with another Exchange account

This branch applies only if all three conditions are true:

• The affected address is an Outlook.com personal account.
• It shares the Outlook profile with another Exchange account.
• You receive a nondelivery report containing error
  0x80070005-0x0004dc-0x000524 or “You do not have permission to send on behalf of the specified user.”

Microsoft documents that exact sending-only problem and reports it fixed at the service level. If it still occurs:

1. Select the Inbox of the Outlook.com account.
2. Select Send/Receive → Send/Receive Groups → Download Address Book.
3. Clear Download changes since last Send/Receive.
4. Select OK.
5. Restart Outlook so it downloads Autodiscover.xml.
6. Send another test message ^5^.

Do not use this branch merely because two accounts are paired; the stated NDR/error is the distinguishing condition.

4. Repair or replace the Outlook profile

If Safe Mode and diagnostics do not resolve it:

1. In Classic Outlook, select File → Account Settings → Account Settings.
2. On the Email tab, select the affected account and choose Repair, if that option is available.
3. Complete the prompts, restart Outlook, and test.

If repair is unavailable or ineffective, create a separate Outlook profile. After creating it, close Outlook, hold Shift while starting Outlook, select the new profile in Choose Profile, and select OK. If sending works, the original profile is damaged ^3^.

If neither webmail nor Classic Outlook delivers messages, contact the email provider and provide the sending time, sender, recipient, subject, and any nondelivery report—without posting those personal details publicly.

References

1. Fixes or workarounds for recent issues in classic Outlook for Windows ...
2. [Classic Outlook](https://support.microsoft.com/outlook/i-can-t-send-or-receive-messages-in-outlook#make-sure-you're-connected-to-the-internet)
3. [Classic Outlook](https://support.microsoft.com/outlook/getstarted/outlook-for-windows-not-responding-hangs-freezes-or-stops-working)
4. Classic Outlook troubleshooters | Microsoft Support
5. Classic Outlook error when sending from Outlook.com "You do not have permission to send on behalf of the specified user 0x80070005-0x0004dc-0x000524." | Microsoft Support