How to Fix Outlook 421 Cannot Connect to SMTP Server Error?

Summary: Outlook users sometimes encounter the error ‘server responded 421 cannot connect to SMTP’. This error usually occurs due to incorrect SMTP settings or blocked SMTP port. In this post, we have provided some effective solutions to fix the error. Also, we’ve mentioned a reliable PST repair tool that can help fix the error, if it has occurred due to PST file corruption.

Outlook users often face an error “the server responded 421 cannot connect to SMTP”, while sending email in Outlook. This error is particularly common in IMAP Outlook accounts that are set up with incorrect SMTP configurations. The 421 error may also occur when Firewall or Antivirus program interferes with Outlook.

Server Responded 421 Cannot Connect to SMTP Server Formats

When facing error 421, you may receive the following messages:

Pro Tip: PST file corruption is a common reason behind the error 421. To repair your PST safely and quickly, use a reliable PST repair software, such as Stellar Repair for Outlook.

How to Fix Error 421 Cannot Connect to SMTP Server?

To fix the error 421, follow the given solutions:

1. Modify SMTP Settings

By default, the SMTP uses port 25. If this port is blocked, you can’t send emails and may encounter the 421 error. To resolve the error, you need to change the SMTP settings.

Follow these steps:

Note: If you can’t open Internet Email Settings window, press CTRL + S + ALT. In the Send/Receive Groups window, click Edit, and select your email account. Then click Account Properties.

Send/Receive Groups window
Changing port numbers in Internet Email Settings window

Next, you need to set Outlook to automatically fetch your mail server’s settings. To do so, follow these steps:

Enabling “Use the same settings as my incoming mail server” option

Now, check if the error is resolved. If the error still persists, proceed to the next solution.

2. Remove and Re-add Email Account

If the error “421 cannot connect to SMTP server” is occurred in a newly added email account, remove the account and then add it again. However, when you recreate the account, make sure that you use the Auto Account Setup and not the Manual setup option (see the image below).

Recreating Outlook account

Follow these steps:

Check if the 421 cannot connect to SMTP error is fixed. If not, move to next solution.

3. Disable Firewall

Windows Firewall regulates Internet access for all the applications on your system. If the Firewall is blocking certain functions of Outlook, such as receiving and sending of emails, it can result in the error: the server responded 421 cannot connect to SMTP.

If the 421 error is caused due to Firewall interference, disabling Firewall can help fix the issue. To do that, follow these steps:

Turning Off Firewall in Windows Settings

4. Check Other Applications

Apart from Firewall, other applications such as VPN or Antivirus may also interfere with the normal functioning of MS Outlook. Disabling such applications can help resolve the 421 cannot connect to SMTP error.

5. Repair PST File to Fix 421 Cannot Connect to SMTP

When Outlook PST is corrupt, it can lead to several errors, including the 421 cannot connect to SMTP error. You need to repair the corrupt PST file to resolve such issues. To repair the PST, you can use Outlook’s in-built utility called ScanPST.exe. It is located in Outlook’s installation directory.

If the PST file is severely corrupt, then ScanPST.exe may fail to repair the data file. In that case, you can use an advanced Outlook repair software, such as Stellar Repair for Outlook. The software can easily repair severely corrupt PST files in a few steps. It’s a powerful tool that can work with even large PST files without any problem. It can recover all the mailbox items, including emails, attachments, contacts, etc.

The following are some main highlights of the PST file recovery tool:

To repair a PST by using Stellar Repair for Outlook and fix Outlook 421 cannot connect to SMT error, follow these steps:

PST selection window in Stellar Repair for Outlook
PST preview in Stellar Repair for Outlook
Selecting PST file format

The repaired PST file will be saved at the provided location.

Conclusion

The error “the server responded: 421 cannot connect to SMT” is a cause of frustration for many Outlook users as it prevents them from sending emails in Outlook. In most cases, the error can be fixed by reconfiguring SMTP settings or disabling Firewall and VPN. In case the issue occurs due to a corrupt PST, you can use Microsoft’s ScanPST.exe utility or Stellar Repair for Outlook software to repair the file.

Also Read:

Related Post

Stellar Data Recovery

Trial Download is for Desktop or Laptop. Put your email id to receive the download link




Exit mobile version