Troubleshooting Error Code 0×8004210e

When users attempt to download their email they sometimes will receive an error message such as:

“Task ‘<Server_Name> – Receiving’ reported error (0×8004210E): ‘Yουr mailbox іѕ temporarily unavailable bесаυѕе another e-mail message іѕ being delivered tο іt οr another mail application іѕ accessing іt. Thе server responded: -ERR box locked”

This error code, 0×8004210e, is sent from your Internet Service Provider and can be a result of a locked mailbox. Sometimes other error messages may appear that refer to a “POP Lock” (Post Office Protocol) or “Box Lock”. These error messages can be received when using email clients such as Microsoft Outlook, Outlook Express, Windows Mail and others.

The error message can be generated because of network problems, malformed email messages, or more than one email client being configured to poll the server. What happens is that the lock file – which is used to stop more than one person from logging into the account at once – fails to be deleted at the end of the POP3 session. It then prevents the end user from logging in again and thus the error code, 0×8004210e is sent.

One resolution is to simply restart your mail client. If your end user cannot wait for a restart, or if a restart is not convenient at the time, then the user can try to access their email from a webmail account. If that fails then the problem may lie with the Internet Service Provider and in that case the administrator should contact the ISP support desk.

If restarting the mail client and contacting the ISP are not successful resolutions then the following workarounds should be tried:

1. Limit the end user’s access to email from only one email client. For the particular end user with the email issue an administrator can restrict the end user’s access to all other email clients. Only Microsoft Outlook access should be allowed for the end user. One method is to disable the other email clients. Another method would be to rename the end user’s account on the other email clients thereby preventing further email messages from being downloaded to that particular client. In addition, email devices such as a Blackberry, iPhone, οr similar device, thаt download the end users email, should also be disabled.
2. Another workaround is to temporarily disable antivirus software and anti-spam software on the end user’s system. Unfortunately by disabling such software on an end user’s system this will render that system vulnerable to computer attacks. This should be the last choice and only be performed temporarily as systems are left open to computer viruses and other malicious programs. The reason why disabling the antivirus and anti-spam software is a workaround is because these software applications installed on the client can have problems with interpreting the email and does not complete. So it doesn’t try to download the next email message from the server. To implement this workaround an administrator can follow this procedure:
   a. All antivirus and anti-spam software should be disabled on the client system. Likewise, disabling any email scanning features should also be performed.
   b. From Outlook, click on Send/Receive to download any malformed email messages from the email server.
   c. Once email has been downloaded then re-enable the antivirus and the anti-spam software on the client system.
   d. Email messages can now be opened.
3. A web email client can be used to access the end user’s email messages and then delete the malformed email from the mailbox. A safe practice would be to target those email messages that are greater than one megabyte in size and then delete them.
4. A fourth workaround is to enable server-side anti-spam and antivirus software on the email accounts using the web control panel. Most malformed emails will be prevented from reaching the end user’s inbox and thus stop the error code (0×8004210E) from being generated.

Administrators should be cautious and fully aware of the risks associated with turning off antivirus and anti-spam software. It would be wise to make a backup of the end user’s system before turning off these applications. And if the end user is accessing their email from within a virtual environment then this will also help to lower the risk of any potential damages.