How to fix macOS Mail app failing to authenticate with Microsoft 365 after changing your password

Summary

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

Common Causes

After changing your Microsoft 365 password, the macOS Mail app may fail to authenticate because it is still attempting to connect using your previous credentials. This typically results in repeated password prompts or a "Account authentication failed" error. Updating the stored credentials within macOS will allow Mail to reconnect to your Microsoft 365 mailbox and resume sending and receiving messages.

Quick Fix Steps

1. Open System Settings.
2. Select Internet Accounts from the sidebar.
3. Click your Microsoft Exchange or Office 365 account.
4. Click Reset Password or Sign In.
5. Enter your new Microsoft 365 password and complete any multi-factor authentication prompts.
6. Restart the Mail app and verify that emails are syncing.

Detailed Instructions

Step 1: Open Internet Accounts

1. Click the Apple menu in the top-left corner of your screen.
2. Select System Settings.
3. Scroll down the left-hand sidebar and click Internet Accounts.

Step 2: Update your Microsoft 365 Account

1. Locate your Microsoft Exchange or Office 365 account in the list on the right.
2. Click the account to select it.
3. If a warning appears stating that the account needs attention, click Reset Password. Otherwise, click the account name or the Details button.
4. When prompted, enter your new Microsoft 365 password.
5. If you have multi-factor authentication enabled, follow the on-screen prompts to approve the sign-in via your authenticator app or SMS.
6. Ensure the Mail checkbox is selected so that the account remains active in the Mail app.
7. Click Done to save the changes.

Step 3: Restart the Mail app

1. Quit the Mail app completely by pressing Command + Q or selecting Quit Mail from the Mail menu.
2. Reopen Mail from your Dock or Applications folder.
3. Wait a few moments for the app to synchronise your folders and messages.

Troubleshooting

Authentication prompt keeps appearing

If Mail continues to ask for your password after following the steps above, your Mac may be storing an outdated password in the keychain.

1. Open Finder, then go to Applications > Utilities.
2. Double-click Keychain Access.
3. Use the search bar in the top-right to search for Office365 or Exchange.
4. Right-click any entries related to your Microsoft 365 account and select Delete.
5. Restart the Mail app and sign in again when prompted.

Mail app is offline or not syncing

1. Open Mail and select Mailbox from the top menu bar.
2. Click Get All New Mail or press Shift + Command + N.
3. If the account remains offline, go to Mail > Settings > Accounts.
4. Select your Microsoft 365 account and ensure the Account is enabled box is checked.
5. Close Settings and restart Mail.

Note: If you use the same Microsoft 365 account on an iPhone or iPad, you may also need to update the password in the iOS Mail app settings under Passwords & Accounts.

Warning: Avoid saving your password in plain text or sharing it via email. If you suspect your account has been compromised, change your password immediately via the Microsoft 365 admin portal.

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