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How to fix outlook error code 421?

While connecting to Outlook Express using a POP3  connection then you need to change server settings of Microsoft Exchange server.

It is common to have an error message while sending or receiving emails on the server. The error message may vary  from computer to computer but you will get below error code commonly:

“An unknown error has occurred: Server error 421”

Common variations of the 421 email error-

  • 421 4.2.1: (DYN:T1) http://postmaster.info.aol.com/errors/421dynt1.html
  • 421 4.3.1 Out of disk space for temp file
  • 421 4.3.2 All server ports are busy
  • 421 4.3.2 All server ports are busy
  • 421 4.4.2 mx.aol.com Error: timeout exceeded
  • 421 #4.4.5 Too many connections from your host.
  • 421 #4.4.5 Too many connections to this host.
  • 421 4.7.0 mx.aol.com Error: too many errors
  • 421 4.7.1: (DYN:T1) http://postmaster.info.aol.com/errors/421dynt1.html
  • 421 4.7.1 POL-T2 http://postmaster.facebook.com/response_codes?ip=74.124.194.252#pol-t Connection refused
  • 421 4.7.1 POL-T2 http://postmaster.facebook.com/response_codes?ip=74.124.194.252#pol-t Connection refused
  • 421 Downstream server error
  • 421 Fork failed
  • 421 Greylisting enabled, please try later.
  • 421 LDAP verification agent temporarily unavailable: Connection failed
  • 421 mail.RemoteDomain.com out of connection slots
  • 421 mx.aol.com Service unavailable – try again later
  • 421 <recipient@RemoteDomain.com> Service not available – too busy
  • 421 Server busy, try again later – psmtp
  • 421 service temporarily unavailable
  • 421 Temporary error (#4.3.0)
  • 421 Too many concurrent SMTP connections; please try again later.
  • 421 Unexpected failure, please try later

Symptoms of Error 421-

  • “Error 421” appears and crashes the active program window.
  • Your PC frequently crashes with Error 421 when running the same program.
  • “Microsoft Outlook Error 421” is displayed.
  • Windows runs sluggishly and responds slowly to mouse or keyboard input.
  • Your computer periodically “freezes” for a few seconds at a time.

Causes of Error 421-

  • Corrupt download or incomplete installation of Microsoft Outlook software.
  • Corruption in Windows registry from a recent Microsoft Outlook-related software change (install or uninstall).
  • Virus or malware infection that has corrupted Windows system files or Microsoft Outlook-related program files.
  • Another program maliciously or mistakenly deleted Microsoft Outlook-related files.

some methods to repair this issue-

Method-1

1. Change the Server Settings to its Maximum Limit

Try changing your server settings. Here set the inbound connections limit at maximum limit.

  • To do this, open Microsoft Exchange Server Administrator utility. The access path of this utility will vary depending on the installation procedure used to set up Exchange Server.
  • Once you open MS Exchange Server Administrator utility, click the ‘Connections’ icon in the left side navigation pane. Now double click the internet mail service icon in the right side pane. As you click it, Properties window will open.
  • Now click the ‘Connections’ tab in the Properties window and then click the ‘Advanced’ button. This will open the configuration window.
  • Here reset the number for ‘Maximum Number of Inbound Connections’ to a high number, its maximum limit. After changing the settings, close all open Exchange Server Administrator program windows to successfully complete the process.

Method-2

2. Download a PST Repair Tool-

If the cause of the error is PST files corruption, then not only will you be locked out of your email account, you are also at risk of losing all the data stored in your email account.

However, the best way to resolve the error and ensure full data recovery is to download a reliable PST repair tool. By running a PST repair tool on your system, you can resolve the error 421 right away. It recovers your data, repairs corrupt and damaged PST files.

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  • rahul singh

    I have already setup new account in outlook, then after I test email, it will appear an error message as below:

    Send test e-mail message: The server responded: 421 cannot connect to SMT

  • Roman Miller

    I am getting a “Server Error: ‘421 Too many messages’ ” error when sending e-mail on Outlook 2010, Why?

  • Gaurav Singh

    please suggest any good PST repair tool.

  • Phillips

    I have already setup new account in outlook, then after I test email, it will appear an error message as below:

    Send test e-mail message: The server responded: 421 cannot connect to SMT
    Please advise

  • Benett Mallinson

    How to Fix email delivery issues for error code 4.4.7 in Office 365 ?