How to fix macOS Mail app authentication errors with Microsoft 365 after changing your password

Summary

This guide helps you troubleshoot and resolve: How to fix macOS Mail app authentication errors with Microsoft 365 after changing your password. Follow the steps below to fix the issue.

Common Causes

When you change your Microsoft 365 password, the macOS Mail app may continue using your old credentials. This often results in repeated sign-in prompts, "Account authentication failed" messages, or emails failing to send and receive. This guide helps Brisbane small business users update their stored credentials and restore normal mail functionality.

Quick Fix Steps

1. Quit the Mail app completely.
2. Open System Settings and navigate to Internet Accounts.
3. Remove and re-add your Microsoft 365 account.
4. Sign in with your new password and complete any Multi-Factor Authentication prompts.
5. Restart the Mail app and verify you can send and receive messages.

Detailed Instructions

Step 1: Quit Mail

Ensure Mail is fully closed before making changes. Select Mail from the top menu bar, then choose Quit Mail, or press Command + Q.

Step 2: Open Internet Accounts

1. Click the Apple menu () in the top-left corner of your screen.
2. Select System Settings.
3. In the left sidebar, scroll down and click Internet Accounts.

Step 3: Remove your Microsoft 365 account

1. In the list of accounts on the right, select your Microsoft 365 or Exchange account (it may appear as "Exchange" or show your email address).
2. Click the Remove button (minus icon -) below the account list.
3. When prompted, confirm that you want to remove the account. Your emails remain stored on the Microsoft 365 server and will re-sync once the account is re-added.

Step 4: Re-add your Microsoft 365 account

1. With Internet Accounts still open, click the Add Account button (plus icon +).
2. Select Microsoft Exchange from the list of account types.
3. Enter your full Microsoft 365 email address and click Sign In.
4. When redirected to the Microsoft sign-in page, enter your new password.
5. If your organisation uses Multi-Factor Authentication, complete the verification step using your authenticator app, SMS, or other registered method.
6. Select which services to sync—typically Mail, Contacts, Calendars, and Tasks—then click Done.

Step 5: Test Mail

1. Open the Mail app from your Dock or Applications folder.
2. Wait a few moments for your folders and messages to synchronise.
3. Send a test email to yourself and confirm it arrives.
4. Reply to the test message to verify outgoing mail is working.

Troubleshooting

Mail keeps asking for the password

• Ensure Caps Lock is off when entering your password.
• Confirm your new password works by signing into Outlook on the web in a browser.
• Restart your Mac and repeat the steps above.

Authentication error after re-adding the account

• Your organisation may require modern authentication. Remove the account again and ensure you select Microsoft Exchange rather than IMAP or POP.
• If your Microsoft 365 account is protected by Conditional Access or app passwords, you may need to generate an app password in your Microsoft account security settings and use that instead of your regular password.

Emails are not syncing

• In Mail, select Mailbox from the top menu, then choose Get All New Mail.
• Check your internet connection.
• Verify that Mail is enabled for the account in System Settings > Internet Accounts.

If you have followed these steps and are still experiencing authentication errors, Open a Ticket with our Brisbane support team.

Still Having Issues?