SMTP 421 not available


Most commonly encountered in Outlook Express.

When trying to send an email message using an email program, and connecting to an exchange server, the following error message may be received:

"An unknown error has occurred. Account: 'SMTP', Server: 'Servername', Protocol: SMTP, Server Response: '421 your.domain.com connection limit reached', Port: 25, Secure(SSL): No, Server Error: 421, Error Number: 0x800CCC67"


1. The maximum number of inbound connections the SMTP server can accept at one time has been reached.

2. An incorrectly configured firewall.

3. Incorrect email settings in Outlook Express.

4. LAN issues.

Solution 1

Restart your computer and then try reconnecting.

Solution 2

See if any firewall software is running. If so, then check your firewall software documentation for more help in troubleshooting firewall problems.

Solution 3

Check your Outlook Express mail settings.

Solution 4

If you have your own mail server or are connecting through a Local Area Network (LAN) then contact your system administrator to check your mail server and LAN settings.


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