Fixing Outlook Error 0x8004210e That Occurs While Sending/Receiving

Outlook error 0x8004210e occurs when users try to send/receive email items to other users which may sometimes create frustration before any users. The error will show the below message:

"Outlook Reported error (0x8004210E) : Your mailbox is temporarily unavailable because another email message is being delivered to it or another mail application is accessing it. The server responded: -ERR [IN-USE] account is locked by another session or for maintenance, try again."

Causes that restrict Outlook from sending mail

  • If some other application has opened Outlook at the same time a user is trying to send/receive.
  • If user's Outlook data file is corrupted.
  • Anti-virus software in your PC may also cause this error.

Manual Solution to Resolve Outlook Error 0x8004210e

  • Make sure, no other applications are using Outlook
  • Uninstall Anti-virus software and similar applications
  • Use Inbox Repair Tool to regain PST with minor damage

Process 1: Close Outlook from every Process using Task Manager

At times even if you're not using Outlook but it is kept open in background by other processes. In that situation you can use Task manager for locating all the processes which has open Outlook. To do that, follow these steps:

  • Right click on Task Bar at the bottom of your computer and then click on Start Task Manager
  • Click on Processes ˃ then select OUTLOOK.EXE ˃ click on End Process button
Click on Processes in Task Manager

Process 2: Uninstall Anti-virus and similar applications

  • Disable some of the Anti-virus software such as: Avast, Mcafee, Bitdefender which are the virus scanners that can interact with Outlook
  • Uninstall spam email remover tool (sy for e.g. Spamihilator, SPAMfighter Pro)
  • Disable file synchronization software such as: iTunes, Goodsync
  • Manage Outlook inbox from the sidebar using Windows gadget such as Sidebar Outlook
  • Disable interaction between Outlook & Skype software(View ˃ Show Outlook Contacts)

Process 3: Scan minor damage from PST

If the data under PST file is damaged with minor corruption then it can be manually re-build, all a user needs to do is to run SCANPST tool for fixing minor corruption from personal Outlook file.


In this article, you will get the list of possible reasons affecting MS Outlook to show an error 0x8004210e. Also, that how to resolve them with the help of simple manual steps such as disabling software that usually interacts with Outlook, closing Outlook from other processes using Task Manager and scanning damaged PST file.