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How to Fix Outlook Certificate Error?

An Outlook security certificate is a digital certificate to secure the emails on Microsoft Outlook. It is basically used to sign the emails in Outlook so that the receiver can be sure that the email has actually come from a legitimate person and has not been intercepted or altered by any other person.So if you are one of the users who is encountering Outlook certificate error, then this could be due to various reasons. In this article, you will find out 3 effective manual solutions on how to fix the Outlook certificate error for free.

Why Do I Encounter Outlook Certificate Error?

  1. The most prominent reason for the error is the invalid security certificate. When you try to connect Outlook to the invalid server, the Outlook Certificate error message will pop up on the screen.
  2. Incorrect date and time also cause the security certificate error on Outlook. Every security certificate has an expiry date. When the date is wrong and exceeds the validity of the certificate, Outlook displays the error message.
  3. Every server has a particular certificate assigned for its domain name. If the Internet Service Provider (ISP) changes the domain name, they will also update it in the certificate. So, if the old domain name remains unchanged, then it can lead to Outlook security certificate error.
  4. Another situation for the Outlook error message is when you enter the wrong hostname. While adding a new email account in Outlook, you should check whether the hostname is correct or not. An incorrect hostname does not allow to establish a connection between the server and the email client.

How do I Fix the Outlook Certificate Error?

  • Verify the Certificate Name
  • Change the Outgoing SMTP Port
  • Use Domain Name of your Hosting as Mail Server

Note: You can easily resolve the Outlook certificate error using the manual methods mentioned in this article. If you encounter any Microsoft Outlook errors like Outlook data file not opening, PST file not showing emails, CRC error, etc., then you should make use of a reliable Outlook PST repair tool. Remo Repair PST is one such utility, which can effortlessly fix the above-mentioned errors with ease. The tool works with a read-only mechanism to repair the PST file corruption to recover all your Outlook emails and other items

Verify the Certificate Name

Whenever you encounter Outlook certificate error, your priority has to check whether the name of the certificate and the mail server is the same or not. For establishing a smooth connection between the mail server and email client, it is necessary to have the name of the mail server and the security certificate.

Follow the steps to verify the name on the certificate.

  1. As the Outlook security certificate error appears, click on View Certificate.
  2. Select the Issued to Name option and check whether the name on the certificate is the same as the mail server.
  3. If both are not the same, change it and then restart the Outlook application.
  4. Note: In case the certificate has multiple names, you can try every hostname one by one. If none of them is appropriate, contact your Internet Service Provider for the correct mail server.

Change the Outgoing SMTP Port

Most of the time, Internet service providers block the outgoing SMTP port (Such as Outgoing port 25). And this leads to the Outlook security certificate error. Therefore, you need to change the server from block port to some other port to resolve this issue. Follow the steps below.

  1. Open MS Outlook and click on the File option.
  2. Choose the Info tab and then click on the Account Settings icon.
  3. After that, select the Account Settings option from the list.
  4. Select your email account and press Change.
  5. Now, click on the More Settings option and go to the Advanced tab.
  6. Change the Outgoing SMTP port and click OK to save the change.

Note: Few Internet service providers block the Outgoing SMTP port. Therefore, you need to change the server to 465 if you want to use SSL port. This way, you can fix the Outlook security certificate error. But, if you are installing a security certificate, choose only a custom security certificate or a certificate assigned only for a particular mail server.

When should I use Unsecure Port?

Various institutions might block some of the mail servers such as POP 995, IMAP 993, and SMTP 465 due to security or privacy reasons. During this scenario, if you want to fix the Outlook certificate error then you should use the non-SSL ports.

Note: The non-secure ports are at risk of data theft. However, they also have some security parameters. POP 110, IMAP 143 and SMTP 587 are the few examples of the non-SSL ports.

Use Domain Name of your Hosting as Mail Server

The hosting providers host a large number of domains. In the case of shared hosting, they provide the same server for various domains. So, the security issue arises because these hosting companies do not renew the SSL certificate for every domain. They only expend the certificate for their domain name.

So, it is suitable to use the domain name of your hosting company instead of your domain name as the mail server.


The above article summarizes how to fix Outlook certificate error, by following the above-listed manual methods you can effortlessly repair the error. Even after implementing the manual methods if the issue precedes, Remo Repair PST is the go-to tool for you. For any further queries regarding the Outlook error, make use of the comment section below.

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Molly Owen

Molly is the Lead Technical Specialist with distinguished knowledge and understanding of Mac computers and operating systems. Being a veteran photographer and video recovery specialist, Molly’s expertise on video formats and file repair has helped restore a lot of videos and cherished memories of users.

As a technical specialist she also believes in learning and spreading knowledge about the current and trending aspects of various media formats, Adobe Photoshop and macOS troubleshooting. A full-fledged learner, caffeine-lover and a firm-believer that technology would make the world a better place.

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