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[Fixed] Outlook Server Responded 421 Error

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Outlook server responded 421 Error

Microsoft Outlook is a well-known and famous application used to store mails, send and receive them along with managing other various tasks through the platform like setting up calendars for meetings, managing contacts, appointments, information, notes, etc.

It is used for both personal and professional use as it does guarantee fast service and strong security. However, even though it is known for its impeccable service, things cannot always go a certain way.

Errors have a way of happening every once in a while and some of the common error messages that pop up when dealing with Outlook are- Outlook server responded 421 which occurs when either one is trying to send an email, receives one, or is reading one.

This error is known to hamper the interaction between servers and prevent the mails from being received or sent.

Outlook Server Responded 421 Error

What causes ‘Outlook Server Responded 421 Error’ error:


  1. One of the main issues for this could be a faulty network or slow internet connection because of which the outlook server responded 421 windows is arising.
  2. There could be a default in configuration settings if the account is newly set up and the provided details might be wrong in settings.
  3. There might be certain types of inbuilt or outer antivirus installed along with or without firewalls which might be preventing the running of this application further due to deriving it as spam or a virus.
  4. There could also be a corrupted file that was either mistakenly received or sent and was then clicked on due to which the window of outlook server responded 421 came up.
  5. One of the other major reasons for this error to arise could also be that the connection with VPN got interrupted or interfered with because the server that one is using might not be considered as a whitelist or accepted mail server.
  6. It could also be that one has activated a system that filters spam but is also the reason why this particular error is highlighted because of its interference. 
  7. Another issue could be that the outlook version installed is either outdated, needs an update, or is not installed correctly or appropriately.
  8. It could also be that the personal storage for outlook data where the files are stored has either run out of space or tried to download a file that exceeds its limit to store a file.

Despite any of these various reasons that do not certainly stop here, the issue and the inconvenience caused could really be problematic and create issues permanently if it does not get dealt with immediately.

One should not fret as these issues might get solved with patience and a little technique if applied properly and get sorted without any external help. We can try to adopt these methods and maybe the issue is not big enough to get prolonged and get fixed right then.

How To Fix Outlook Server Responded 421 Error:


1.Try to re-install the outlook application-

As the reasons have already been mentioned above, if the real issue of this is a badly installed version of outlook then it should be fixed within a few minutes. Try to remove then re-install the outlook and see if the error resolves. 

2.Go through the configuration settings-

Try to go through the SMTP settings and follow these steps- 

  • Go to setting on your mail account
  • Review account settings
  • Open the email account on which the issue occurred and the one that you need to edit.
  • Click on the change sync settings option and go through the given details
  • In your outgoing mail server, add:26:1 and click on save after ticking all boxes with yes. 
  • Try to refresh and check your mail server again.

3.Re-add your email account- 

Go through the settings where all your email accounts are added and click on the email account where the error is occurring, remove your email account from there and then enter the details again and re-add it.

4.Look for VPN interruption or interference in settings-

Try to disable the current VPN connection and then check again if the problem still persists, if not then that is where the issue was as it was being blocked because of your VPN connection. Try to contact the customer care in that case and ask them to look through the mail server issue and give it allowance or have them categorize it into a whitelist.

5.Check through your firewall connection-

Go through it and see if disabling it works and helps your mail server respond properly this time or if it is still not fixed.

6.Deal with the maximum limit-

Go through your server’s maximum limit to store data and information and increase its limit to the maximum. One can do this on their own by going to the MS exchange server administrator.

7.Other ways to fix it-

If none of the above helps you out, then one can also try looking for various other tools and call for actions available on the web. However, one should keep in mind that there can be paid subscriptions for it as well before opting for this method.

Before worrying or panicking, know that one can always contact their customer care or get external help and the issue should be resolved from their end.

We hope by now you have effectively solved the issue of Outlook Server Responded 421 Error.

However, if the above-mentioned methods fail to work then we will have to contact Online Technical Support (Call @+1 (878)-999-8893  TOLL-FREE)for help.

We provide 24/7 services with customer support and guarantees customer satisfaction. Best solutions are provided just by sitting at home and solving the error issue with the help of expert professional technicians.

You can also watch our video for more help:

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