Outlook keeps trying to send a nonexistent message while Outbox folder shows zero messages


You experience one or more of the following problems when you use Outlook:

  • Outlook continuously displays a message such as "Sending message 4 of 6" in the Progress bar even though there are no email messages queued. Additionally, Outlook stops responding when you try to close it. For example, you see the following message in the Progress bar:

    Screenshot of the Outlook status bar, which displays a message: Sending message 4 of 6.

    You may also receive an error message that resembles the following:

    Task 'user@example.com - Sending' reported error (0x8004210b) : 'The operation timed out waiting for a response from the sending (SMTP) server. If you continue to receive this message, contact your server administrator or Internet service provider (ISP). The server responded: 550 5.1.0 <> sender rejected. AUP#O-1580'

    Screenshot of the Outlook Send/Receive Progress dialog box, which displays a sending error.

  • You are continually prompted to log in to internet email.

  • Outlook displays a number next to the Outbox folder (for example: Outbox [4]) even though there are no messages in the Outbox.


These problems are caused by a read receipt that is stuck in progress and that Outlook keeps trying to resend.


Use the MFCMAPI tool to delete the stuck messages. To do this, follow these steps:


Make sure that Outlook is closed during this procedure.


If you have the 64-bit version of Outlook installed, you must install the 64-bit build of the MFCMAPI tool.

  1. Download and install the MFCMAPI tool.
  2. Open the MFCMAPI tool, and then select OK.
  3. Select the Session tab, and then select the Logon option.
  4. In the window that opens, select the Outlook profile, and then select the OK button.
  5. Double-click the account that's experiencing the problems (it shows a small cylindrical icon next to the name).
  6. Right-click Root Mailbox, and select the Open contents table option.
  7. In the next window, examine the columns, such as From, To, and Subject. Under Subject, if you see something called Read, or if you see a message that has "Read" as the subject, select that item, and then select Actions > Submit > Abort submit.
  8. Right-click the Delete message option, select Permanent delete passing DELETE_HARD_DELETE (unrecoverable) option, and then select OK.
  9. If you cannot right-click the Delete message option, delete the message that contains the read receipt subject.
  10. Repeat steps 6–9 for each read receipt that you have to delete.
  11. Restart Outlook, and check its behavior.