Outlook Error 0x8004210B – How to Fix It

Did you encounter error 0x8004210B when trying to send a message in Outlook email client and the message was not sent successfully due to the error? If you experienced this problem, the error most likely looked like this.

Task 'email@vasadomena.si - 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).''

Most of the time the problem is that Outlook keeps displaying a notification about a message being sent, for example “Sending message 4 of 6”, even though there are no emails in the queue. It may also happen that Outlook does not respond when you try to close it.

How to fix Outlook error 0x8004210B?

As this is a fairly general error that does not indicate a specific problem, there are several ways to fix the error. We advise you to try the solutions described below:

1. Specify the appropriate port for the outgoing server (SMTP)
2. Temporarily disable the anti-virus program
3. Check the correct spelling of the email addresses
4. Delete the “stuck” email

1. Specify the appropriate port for the outgoing server (SMTP)

Make sure that all settings for the email account are correctly configured. One of the reasons for the error message 0x8004210B could be an incorrect port number for the outgoing server (SMTP). For example, you have set the port number to 465 (port number for encrypted connection), but you forgot to specify the type of encrypted connection in the drop-down menu: SSL.

If this is the cause of the problem, enable SSL encryption on port number 465 during the settings for the email account. If you do not want to use SSL encryption, specify port number 587.

A similar problem, which causes error 0x8004210B in Outlook, can occur if you select TLS from the outgoing server (SMTP) encryption drop-down menu and set the port number to 465. The port number for SSL/TLS encryption is actually 465, but what TLS means in the Outlook client is actually STARTTLS.

STARTTLS is not an encryption protocol, but a command to run TLS. Unlike SSL and TLS, STARTTLS runs on unencrypted ports. So if you have TLS selected, set the port number for the outgoing server to 587. Alternatively, you can leave the port number at 465, but in this case change the encryption protocol from the drop-down menu to SSL.

2. Temporarily disable your antivirus software

The reason for the problems with Outlook error 0x8004210B may also be related to your antivirus software. We advise you to:

1. Close the Outlook email client.
2. Temporarily disable antivirus protection.
3. Reopen Outlook and check if the problem is fixed.

If you can now send emails, this definitely means that the problem is related to the anti-virus software. With some antivirus programs you can disable scanning of outgoing (and incoming) emails.

One of the more well-known antivirus systems that is known to cause Outlook error 0x8004210B is Norton Internet Security or Norton AntiVirus.

3. Check that your email addresses are spelled correctly

Outlook error 0x8004210B may occur due to an incorrect record of the email address in the list of email recipients. The solution is therefore to check the email addresses to which you want to send the email message and make sure that they are all spelled correctly.

This error can also occur in combination with 501 Too many syntax or protocol errors. In particular, make sure that the recipients’ e-mail addresses do not include special characters such as various brackets and parentheses and quotation marks. Alphabetic characters can also cause problems.

4. Delete the “stuck” email

Another cause of Outlook error 0x8004210B is a failed e-mail message that remains stuck in the Outbox or even the Sent Items folder. This could be due to a damaged or oversized attachment.

In this case, we advise you to do the following:

1. Select the Send/Receive tab at the top of Outlook.
2. On the right-hand side you will find the Work Offline icon – click on it.
3. Navigate to the folder where the problem message is located. Right-click on it and delete it ( Delete).
4. Edit the attachment that caused the error.
5. Close and reopen Outlook.
6. Click on the Work Offline icon to disconnect the offline work so that the programme is connected to the internet again.
7. Try sending the message again.

We are confident that you will be able to resolve Outlook error 0x8004210B using any of the methods described.

For further assistance, please call us on 059 335 000 or email us at info@neoserv.si.