How To Fix Outlook Certificate Error in Office 365

Fix Outlook Certificate Error in Office 365 quickly and securely by understanding the root causes and applying step-by-step troubleshooting.

Outlook certificate errors are common when email clients face SSL/TLS issues, incorrect DNS records, or untrusted certificate authorities.

This guide provides detailed solutions to help users resolve errors efficiently and maintain uninterrupted, secure communication through Microsoft Outlook.

Before diving into fixes, you should verify the certificate name first.

view-certificate-name-outlook

To do so, go to the pop-up error message and click on the view certificate. Navigate to the “Issued to Name” option and confirm whether the name indicated on the certificate matches that of the mail server.

security-certificate-information

If there is a disparity, correct the information and then restart Outlook.

Now, let’s move on.

fix-outlook-certificate-error

What Is an Outlook Certificate Error and Why It Happens?

An Outlook certificate error occurs when the mail server’s SSL certificate cannot be verified. This often happens when:

  • The certificate has expired
  • The name on the certificate doesn’t match the server domain
  • The certificate authority is untrusted

These errors prevent Outlook from establishing a secure connection.

How to Fix Outlook Certificate Error: Step-by-Step Guide

Here’s how we fixed the Outlook certificate error:

1. Fix Autodiscover DNS Records (Internal, External, or Both)

Autodiscover helps Outlook find mailbox settings automatically. If DNS records are incorrect, certificate validation will fail.

So, why is this feature so important?

Actually, it’s a bit complicated. Let us explain this scenario in the easiest manner possible.

Autodiscover is a feature in Microsoft Exchange that automatically configures user profile settings for clients like Microsoft Outlook. It simplifies the setup process by automatically discovering and configuring the necessary server settings, eliminating the need for users to manually input details like server names, ports, and encryption methods.

In terms of DNS records, Autodiscover relies on specific DNS entries to locate the Autodiscover service.

These DNS records typically include the Service (SRV) record and the Autodiscover domain (CNAME) record.

Check SRV Record

The SRV record helps the client find the Autodiscover service endpoint, while the CNAME record points to the domain where Autodiscover settings can be retrieved.

Follow the steps below to change the autodiscover DNS records:

  1. Open the command prompt or Windows PowerShell.
  2. Run the nslookup command:
    nslookup -type=srv _autodiscover._tcp.yourdomain.com
    Here, replace yourdomain with the name of the domain from the issued certificate.
    security-certificate-information
  3. Check A or CNAME Records (Optional) using the following command:
    nslookup autodiscover.yourdomain.com
  4. Update DNS records by running the NSLOOKUP with
    nslookup set type=srv _autodiscover._tcp.yourdomain.com
  5. Enter the new values as prompted
  6. Type exit to close the NSLOOKUP session.

Note: Remember to replace yourdomain.com with your actual domain, and ensure you have the necessary permissions to update DNS records.

When an Outlook client utilizes the SRV record, it may prompt the user with a notification about the upcoming redirection. It is advised for the user to select the option “Don’t ask me about this website again” to prevent the recurrence of this message.

server-redirection-notice

2. Disable Outlook Add-ins Causing Conflicts

If your Outlook is showing problems after you installed a third-party add-in then this solution is for you.

Press the Windows+R key to open the RUN dialog box. Now type outlook/safe to open Outlook in safe mode.

outlook-safe-mode

Now go to File> Options>Add-ins. Select COM Add-ins from the Manage dropdown menu at the bottom of the tab and click on GO.

choose-add-ins-from-outlook-options

Uncheck any faulty or unwanted add-ins and restart outlook.

uncheck-outlook-faulty-add-ins

3. Use Non-SSL Ports If SSL Ports Are Blocked

Certain networks, especially in educational institutions, may block SSL ports for email servers, leading to an Outlook security certificate error in Office 365.

To address this, users can consider using non-SSL ports, such as POP 110, IMAP 143, and SMTP 587, which might not be blocked on the network.

change-ssl-ports

It’s emphasized that while these non-SSL ports offer a workaround, they come with a potential risk of data theft.

4. Use Hosting Domain Name as Mail Server

If you use shared hosting, the SSL certificate may not cover your domain. Instead, use the provider’s domain (e.g., mail.hostingprovider.com) in your email settings.

This is suggested due to potential security issues arising from shared hosting providers not consistently renewing SSL certificates for each individual domain hosted on the shared servers.

How to Enable SSL in Outlook

Enabling SSL in Outlook is crucial for ensuring the security and privacy of your email communications.

SSL is a protocol that encrypts the data exchanged between your email client (Outlook) and the email server, making it significantly more challenging for unauthorized parties to intercept and decipher the information.

By using SSL, you create a secure, encrypted connection for both incoming and outgoing email servers.

Here are the steps to enable ssl in outlook:

  1. Open Outlook and navigate to File > Account Settings > Account Settings.outlook-account-settings
  2. Choose your email account and click Change.
  3. Adjust the Incoming mail server and Outgoing mail server (SMTP) settings to mail.example.com, replacing “example.com” with your actual domain name.
  4. Click on More Settings.
    adjust-outgoing-mail-server-smtp
  5. In the Advanced tab, for IMAP accounts, set Incoming Server (IMAP) to use SSL and Outgoing Server (SMTP) to use SSL. For POP3 accounts, check the box for “This server requires an encrypted connection (SSL)” under Incoming Server (POP3) and set Outgoing Server (SMTP) to use SSL.
    set-incoming-and-outcoming-server
  6. Click OK.
  7. Click Next and then Finish to complete the email account configuration.

Types of Outlook Certificate Error Messages

According to our compiled data, there are 3 types of certificate error messages.

  1. Type 1
  2. Type 2
  3. Type 3 Error

Type 1 Error Message (Certificate Name Mismatch)

type-1-outlook-certificate-errorIssue: The proxy server’s security certificate has a name mismatch or does not align with the site’s name, preventing Outlook from establishing contact with the proxy server.

Error Code: 0

Type 2 Error Message (Invalid Certificate Authority)

type-2-outlook-certificate-error

Issue: A problem persists with the proxy server’s security certificate, causing Outlook to be unable to connect to the specified proxy server (e.g., mail.matc.net).

Error Code: 00000000

Type 3 Error Message (Expired or Revoked Certificate)

type-3-outlook-certificate-error

Issue: The security certificate is from an untrusted certifying authority, indicating that the certificate was issued by a company that the user has not chosen to trust. The user is prompted to view the certificate and decide whether to trust the certifying authority.

Error Code: 00000000

Fix Outlook Certificate Error After Windows 11 Reset

After a reset, Windows may forget your saved settings. Ensure DNS records are correct and SSL certificates are installed properly.

Still facing issues after trying everything above? You might be experiencing a different type of Outlook problem. Learn how to fix the Outlook 500 error here.

Troubleshoot Outlook Certificate Error on iPhone or Mac

On iPhone:

  • Update mail server settings
  • Trust the certificate manually under Settings > General > About > Certificate Trust Settings

On Mac:

  • Open Keychain Access
  • Locate the certificate, open it, and mark it as trusted
  • Restart Outlook for Mac

Frequently Asked Questions

Question: What is an Outlook certificate?

Answer: An Outlook certificate, often referred to as an SSL (Secure Sockets Layer) certificate or a digital certificate, is a security feature that enables secure communication between Outlook and the email server. It encrypts the data exchanged between the email client (Outlook) and the mail server. The main reason for installing an Outlook certificate is that sensitive information, such as login credentials and email content, remains private and secure.

Question: What causes Outlook certificate errors?

Answer: Certificate errors in Outlook typically occur when there’s an issue with the SSL certificate configuration. Some reasons include: Expired SSL certificates, incorrect certificate configuration, self-signed certificates, missing certificate chain, and revoked certificates. When Outlook encounters a certificate error, it typically warns the user and provides options to proceed or reject the connection.

Question: Is it safe to use non-SSL ports?

Answer: Non-SSL ports may temporarily resolve issues but expose your emails to risk. Always revert to SSL-enabled ports for secure communication.

Question: What is Autodiscover?

Answer: Autodiscover is a Microsoft Exchange feature that allows Outlook to auto-configure your account using DNS records and eliminate manual setup.

Final Words

This comprehensive guide equips users with insights and solutions to tackle Outlook certificate errors comprehensively.

Resolving Outlook certificate errors demands a nuanced approach, considering various factors such as Autodiscover DNS records, add-ins, network configurations, and SSL usage.

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