📘 Summary

If your Microsoft email account (Outlook.com, Hotmail, Live, MSN) has suddenly stopped syncing or is showing authentication errors in Mailbird, this is due to recent changes on Microsoft’s side—not an issue with Mailbird itself.

This guide walks you through the most effective solutions to restore access.

⚠️ What’s Happening

As of March 2026, Microsoft has accelerated the deprecation of Basic Authentication for personal email accounts. At the same time, a Windows update bug (KB5079473, released March 10, 2026) disrupted OAuth sign-ins for these accounts.

Together, these changes are causing widespread authentication failures across all third-party email clients—not just Mailbird. The same behavior has been confirmed in other applications, including Mozilla Thunderbird.

🛠️ Fix 1: Install the Windows Emergency Update (Recommended)

Microsoft released an emergency update (KB5085516) on March 21, 2026 to resolve the OAuth sign-in issue. More information can be found here, but please keep in mind that Microsoft has made this emergency update compatible for Windows 11 only.

1. Open Settings → Windows Update
2. Click Check for updates
3. Install KB5085516 if available
4. Restart your PC
5. Open Mailbird and check if your account reconnects

📩 Fix 2: Enable IMAP Access in Outlook.com

Microsoft now requires IMAP access to be explicitly enabled—even when using modern authentication.

1. Log in at https://outlook.live.com
2. Click the ⚙️ Settings icon → Mail → Forwarding and IMAP
3. Click Sign in if prompted
4. Scroll to the POP and IMAP section
5. Enable:
   • “Let devices and apps use IMAP”
   • “Let devices and apps use POP”
6. In Mailbird, remove and re-add your Microsoft account

🔐 Fix 3: Use an App Password (For MFA Accounts)

If Multi-Factor Authentication (MFA) is enabled on your Microsoft account, you may need to use an app-specific password.

1. Go to https://account.live.com/proofs/manage
2. Navigate to Advanced security options
3. Under App passwords, click Create a new app password
4. Copy the generated 16-character password
5. In Mailbird, go to Settings → Accounts
6. Select your Microsoft account
7. Choose Username and password authentication
8. Paste the app password instead of your regular password

🔒 Fix 4: Verify TLS 1.2 is Enabled

Microsoft requires TLS 1.2 for secure connections.

1. Open Control Panel → Internet Options
2. Go to the Advanced tab
3. Scroll to Security
4. Ensure Use TLS 1.2 is checked
5. Click OK and restart Mailbird

🧱 Fix 5: Check Security Software Interference

Security tools such as antivirus software, firewalls, VPNs, or proxies can interfere with OAuth authentication.

1. Temporarily disable your security software
2. Attempt to reconnect your email account in Mailbird
3. If successful, add Mailbird as an exception (i.e. whitelist) in your security settings

ℹ️ Why This Isn’t a Mailbird Issue

These authentication problems are caused entirely by changes in Microsoft’s infrastructure. The same issues occur across multiple third-party email clients, confirming this is not specific to Mailbird.

Microsoft has acknowledged the OAuth-related issue and released a fix via update KB5085516.