How to Fix an Outlook Express Error 421

Microsoft Exchange Server administrators may need to change the server settings if users connect to the server with Outlook Express using a POP3 connection. The users will receive an error message when they try to send email to an email account on the server. The message may vary but will typically begin with "An unknown error has occurred" and specify "Server Error: 421." The error occurs when the number that has been set for maximum inbound connections on the server is met. To resolve the problem you must increase the number of connections allowed.

Difficulty: Moderately Easy

Instructions

1. Open the Microsoft Exchange Server Administrator utility. The access path to the utility will vary depending on the installation procedure used to set up your Exchange Server.

2. Click the "Connections" icon in the left-side navigation pane of the Microsoft Exchange Server Administrator window for the server you want to administer. Double-click the Internet Mail Service icon in the right-side pane. This opens the Properties window.

3. Click the "Connections" tab in the Properties window, then click the "Advanced" button. This opens a configuration window.

4. Set the number for "Max No. of Inbound Connections" to a high number such as 100. You may need to reset it to higher values until the problem is resolved.

5. Close all open Exchange Server Administrator program windows to complete the process.

References

• Article on Microsoft Website about resolving an Outlook Express Error 421 message