How To Fix Outlook 421 Cannot Connect To SMTP Server Error

Encountering Outlook 421 Cannot Connect To SMTP Server Error?? Don’t worry and instead go for the methods discussed here in this blog… as they guarantee to fix this particular MS Outlook error.

OK… so before coming on how to fix Outlook 421 Cannot Connect To SMTP Server Error or Outlook cannot connect to your outgoing (SMTP) e-mail server… it’s important to provide you with a quick glimpse of what this Outlook error is actually and what are the causes behind its emergence…

So, here we go…

Server Responded 421 Cannot Connect to SMTP Server Error

‘Server Responded: 421 cannot connect to SMT/SMTP server’ error arises when trying to send an email in Outlook.

This error particularly occurs in IMAP Outlook accounts which are set up with inappropriate SMTP configurations.

Moreover, the 421 error might occur when the Antivirus program existing on the PC interferes with Outlook.

Outlook 421 Cannot Connect to SMTP Server Error Formats:

When facing error 421, you might see the set forth error messages on your screen:

• The server responded 421 cannot connect to the SMTP server
• The server responded: 421 cannot connect to SMT
• Could not send your message: Error 421
• An unknown error occurred: Server Error 421

Causes of Outlook Cannot Connect To Your Outgoing (SMTP) E-mail Server

Outlook Configuration Mistakes

The most prominent reason for the Outlook Cannot Connect to SMTP/SMT server error is a configuration mistake in Outlook settings. Nonetheless, this is only applicable, in case if the issue appeared with a newly configured email account.

Antivirus-related Issues

This behavior doesn’t happen with the built-in Windows firewall. Nonetheless, some 3^rd party firewalls and antimalware suites are configured to block connection to several IP ranges… this includes the email server.

Filtered Traffic on Port 25

Another common practice implemented by ISPs to minimize automated spam is to block traffic via port 25. Now though this is effective in preventing the contaminated PCs from acting as SPAM networks… however, also creates lots of issues for the end-user, including the 421 Cannot Connect to SMTP Server Error.

Interference Caused by a VPN Connection

Some VPN providers do not have the email server which you used whitelisted. This triggers the ‘Server Responded 421 Cannot Connect to SMTP Server’.

So, these were the causes behind the occurrence of Outlook 421 Cannot Connect to SMTP Server error.

Now relying on the causes… one can go for the appropriate solution to fix this Outlook error.

As promised above, here below we have listed numerous methods to fix this SMTP server error. These methods are the ones… successfully deployed by users to deal with outlook cannot connect to your outgoing (SMTP) e-mail server or SMTP error (421) connection to server failed cpanel.

How To Fix Outlook SMTP Error 421

Method 1: Reconfigure SMTP Settings

One of the most probable causes behind outlook error code 421 or outlook cannot connect to your outgoing (SMTP) e-mail server is improper SMTP configuration, as mentioned above…

Thus, checking the SMTP configuration is the first method recommended to fix the issue ‘could not connect to SMTP host response: 421’

In order to reconfigure SMTP settings in MS Outlook, implement the set forth steps:

• Launch MS Outlook
• Click File

• Click Account Settings

• Select your account and then click Change

• Locate ‘Outgoing mail server (SMTP)’ and then enter the address (provided by your web host)

• Locate and click More Settings
• Navigate to the Outgoing Server
• Check the My Outgoing Server (SMTP) requires authentication
• Select the Use the same settings as my incoming mail server

• Go back to the More Settings window and then click Advanced
• Under the Advanced tab, locate and change your port number (provide by your Internet Service Provider)

• Save Settings and then close the program
• Check if the error is fixed: open up Outlook and try sending an email.

Hopefully, this method will for sure help you out on ‘How To Fix Outlook 421 Cannot Connect to SMTP Server Error’…. Nonetheless, if not, we request you to go for the next method…

Method 2: Check your VPN (Fix SMTP Response 421)

As everyone knows, VPNs are to mask locations and gain access to geo-blocked/geo-restricted websites services, especially from restricted areas.

Up to some extent, this VPN may interfere with your browsing behavior, including your access and transmission of emails in Outlook.

Now though this VPN has little or no direct influence on email transmission… however its interference with Internet-based programs such as Outlook is not common.

Thus, you can check if the error is due to interference from your VPN by simply disabling it for few seconds.

After disabling your VPN service, you can try to send an email.

If the email goes through without any issue… the VPN is probably the cause of the issue.

This method is one of the finest ways to fix sending’ reported error (0x800ccc67) ‘ the server responded 421 cannot connect to SMTP server.

Method 3: Disable Firewall or Antivirus (Resolve: could not connect to SMTP host response: 421)

Windows Firewall does regulate Internet access for all the applications on your system.

In case if the Firewall blocks certain functions of Outlook, like sending and receiving of emails, it results in an error:

Server responded 421 cannot connect to SMTP or could not connect to SMTP host response: 421 or SMTP error (421) connection to server failed cpanel.

Now either of these errors (though all the same) is due to Firewall interference, then disabling Firewall can help to fix this Outlook Error 421.

To Disable Firewall, Follow the Set Forth Steps:

• Go to the Start menu and then open Control Panel
• Open up System and Security and then click Windows Firewall.
• Click Turn Windows Firewall on or off.
• Turn off the Firewall under both private and public network settings. Click

Method 4: Remove and then Re-add Email Account

If the error ‘421 cannot connect to SMTP server’ occurs in a newly added email account… what you need to do is ‘Remove the account and then add it again’.

Nonetheless, when you recreate the account… you need to assure that you use the Auto Account Setup and not the Manual Setup option.

Implement the set forth steps:

• Firstly, launch Outlook and then go to File > Account Settings
• Select the email account which is causing the error and then click Remove
• Click the New button and then enter the email account’s credentials.
• Click Next and then wait till the account is set up.

Check if the could not connect to SMTP host response: 421 or SMTP error (421) connection to server failed issue get resolved or not… If not… move to the next method…

Remember, it’s the last, but of course not the least.

Method 5: Repair PST File To Fix Outlook 421 Cannot Connect to SMTP Server Error

PST file, an Outlook data file that stores local copies of messages, calendar events, and other items from your Exchange mailbox… is an important aspect of the MS Outlook application.

Corruption of these PST files leads to various errors, including 421 Cannot Connect to SMTP server.

So, one of the finest ways on how to fix Outlook 421 Cannot Connect to SMTP Server error is repairing the PST file…

Now, regarding the repairing of the PST file, Scanpst.exe (Outlook’s in-built utility, located in the Outlook’s installation directory) can get used…

However, in case if it gets fails, you should go for an Outlook Repair Tool.

Now, despite the fact that today in the market there is the wide availability of Outlook PST Recovery Software, it’s strongly recommended here to go for Stellar Outlook PST Recovery Software (aka Stellar Repair for Outlook).

Packed with highly powerful and enhanced algorithmic skills, Stellar Outlook PST Repair Tool very easily and efficiently repair severely corrupted PST files in just a few steps.

The tool includes the potential of recovering even the large PST files, without any problem.

The tool can recover all the mailbox items, including emails, contacts, attachments and etc.

Salient Features of Stellar Outlook PST Recovery Software

• Recovers mailbox from large PST
• Restore deleted Outlook mailbox items
• Provides a preview of the recoverable data.
• Easy and quick recovery of Outlook PST.
• Split or Compact PST & export to Office 365.

>>Stellar Repair for Outlook Free Download<<

OK… so here finally ends up… how to fix Outlook 421 Cannot Connect to SMTP Server Error or sending’ reported error (0x800ccc67) ‘ the server responded 421 cannot connect to SMTP server or SMTP error 421 connection to server failed.

Hopefully, you enjoyed reading the blog and got satisfactory answers to your questions.

Nonetheless, if still queries existing… kindly feel free to ask in the comment section below.

Thanks!!