Exchange Connection Problems

How to Fix Outlook Certificate Warnings for Trusted Sites

Adam Davis Sep 29, 2026 868 views

Question details

The user needs to stop recurring security and certificate warnings in Outlook that persist even when connecting to trusted mail servers.

How to Fix Outlook Certificate Warnings for Trusted Sites

Product: Microsoft Outlook
Device & OS: not provided
Scenario: Managing email account configurations and resolving repeated security certificate prompts.
Observed behavior: Outlook continuously displays certificate warnings or hostname mismatch errors due to lingering credentials, outdated profiles, or conflicting add-ins.

Before you start

Ensure you have the correct incoming and outgoing mail server settings from your email provider, and save any pending drafts before making changes to your profile.

Solution 1Recommended

Remove Old Accounts and Rebuild Outlook Profile

Clear outdated email configurations and profiles that might be triggering the certificate mismatch.

Often, Outlook continues to reference configuration data from an old email account even after it has been removed from the main interface. Clearing these entries from the Control Panel is the most effective way to stop the warnings.

Close Outlook

Ensure Microsoft Outlook is completely closed before modifying profile settings.

Access Mail Settings

Open the Windows Control Panel, change the view to Large Icons, and click on 'Mail' (or 'Mail (Microsoft Outlook)').

Remove Old Accounts

Click on 'Email Accounts'. Select any obsolete or old email accounts from the list and click 'Remove'.

Clear Data Files

Switch to the 'Data Files' tab in the same window and ensure no lingering data files from the removed account remain. Remove them if present.

Create a New Profile

If the issue persists, return to the main Mail setup window, click 'Show Profiles', click 'Add' to create a new profile, and set it as the default.

Profile Refresh: Creating a new profile ensures all background connections to old, mismatched servers are permanently severed.

Solution 2

Clear Windows Credential Manager

Remove saved passwords that might be forcing Outlook to silently connect using outdated credentials.

Solution 3

Verify Hostnames and Check Add-ins in Safe Mode

Determine if a third-party add-in is causing the security warning and manually verify server hostnames.

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Frequently Asked Questions

Why does Outlook say the target principal name is incorrect?

This warning occurs when the hostname on the SSL certificate provided by the mail server does not match the server address configured in your Outlook account settings. Updating your incoming and outgoing server settings to perfectly match the certificate's domain usually resolves this.

Will creating a new Outlook profile delete my existing emails?

No, creating a new profile simply establishes a fresh connection to your mail server. For IMAP and Exchange accounts, your emails remain safely stored on the server and will automatically sync to the new profile once connected.

How do I find the correct mail server settings to fix the certificate warning?

You can usually find the correct incoming and outgoing server names, along with the required SSL port numbers, in the online support documentation provided by your email hosting provider or by contacting your company's IT department.

Outlook & Email Problems