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

Please let me know that How to Fix Outlook Error 421, Cannot Connect to SMTP Server. I am facing some issues while using Outlook. Help me.

Cyrus Neal 1   Ans 4 months ago
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Fix Outlook Error 421, Cannot Connect to SMTP Server:

Microsoft Outlook is the best web app at the present time. The main function of this app is to manage and organize the personal information of the users. This includes notes, appointments, tasks, contacts, emails, etc. Additionally, this program has improved and better security features.

This is the main reason why various users trust and use MS Outlook. It relies on three email protocols POP, IMAP, and SMTP. These protocols are prone to technical issues. This mainly happens because of wrong configuration or problems with the server port. This includes recovery mail from the junk mail folder of Outlook.

Moreover, it includes, the "Cannot read from the source file or disk" error in Outlook. One of the common issues is Outlook 421 cannot connect to the SMTP server. This problem can be resolved with the right solutions in no time. 


The Simple Mail Transfer Protocol is also known as the SMTP server.  This is an email protocol that mainly deals with the outgoing function of email. This protocol allows users to transfer messages and emails over the internet. Even a small problem in the SMTP settings can deeply impact the basic functions of sending emails. 

Causes of Outlook 421 error

There are various reasons responsible for this error. 

  • A bug or virus leads to the malfunction of the system.
  • Wrong configuration of a newly-setup email account. 
  • Problems with the server port settings
  • Antivirus programs have some issues and risk. 
  • Some corrupt PST files in Outlook. 

Different Ways to Fix Outlook Error 421-

Firstly, you need to ensure that you have a stable internet connection with sufficient bandwidth and high speed. Also, make sure that there are no interruptions like a power failure. Then, try the solutions mentioned below one by one. 

1) Reconfigure Your Email Account

Whenever this issue occurs, one of the solutions that you can try is to remove the account that presently exists. Reconfigure the same by using auto account setup. This will definitely help you in fixing your problem.

Below are the steps that you need to follow to reconfigure your email account. 

Step 1: Launch MS Outlook and then select files

Step 2: After that, visit account settings under the same tab. 

Step 3: Choose the current email account and then select Remove in order to disconnect it from  Outlook. Then, click on New to add email. 

Step 4: Then, you are required to enter the necessary details and then select Next. This will complete the email configuration process. 

2) Disable Antivirus Programs

There is a chance that the antivirus program you are using may consider your server connection as a possible threat. Because of this, it is blocking and restricting some functions in Outlook.

This may also lead to error 421, where Outlook is not able to connect to the SMTP server. Please ensure that you disable all possible programs that may get in the way of your SMTP connection. 

3) Reset Your SMTP Server Port

A server port helps in determining the right path and endpoint of a message. Even a small problem can lead to server connection issues.

Below are the steps that you need to perform in order to reset your SMTP server port. 

Step 1: Go to the "Files" section and then go to "Account Settings".

Step 2: After that, go to your email account and then select Change. 

Step 3: Go to "More Settings" and then select the "Advanced" tab.

Step 4: Reset the outgoing server as 465 and then select OK. 

Step 5: After that, go to the Settings option. 

Step 6: Below the Outgoing Server tab, choose the checkbox "Use the same settings as my incoming mail server and then select OK. 

4) Repair PST Files


This is the storage space for the data of the user. Therefore, it is important to deal with a damaged or corrupt PST file. This can be the actual cause of error 421. In such cases, it is always recommended to use professional tools such as Outlook PST repair.

Below are the steps that you need to follow in order to repair PST files. 

Step 1: Install the kernel for Outlook PST repair on your system. 

Step 2: Choose to browse to select single or multiple PST files as per your needs. 

Step 3: Now, you will see the preview of all the items in the PST files. 

Step 4: Go to the right panel and then select PST for saving information in the same format. 

Step 5: This tool will allow you to filter items. Apply these filters as per your requirement. 

Step 6: You can also split a newly-repaired PST file. Select a splitting option if required. 

Step 7: Select Browse for selecting a destination to save the repaired files and then select Finish.

Mick Jone 01 September 2022