Fix Outlook Error 0x800ccc90: Step-by-Step Guide

Outlook error 0x800ccc90 typically appears when the program cannot connect to your email server, often due to incorrect authentication settings, an outdated password, or a corrupted mail profile. The fix usually involves verifying your login credentials, checking your server settings, and rebuilding the Outlook profile if the problem persists. Below is a detailed guide to resolving this error on current versions of Microsoft 365 and standalone Outlook.

What Causes Error 0x800ccc90?

This error is part of the 0x800CCCxx family of Outlook connection errors. It specifically indicates that the client could not authenticate with the incoming or outgoing mail server. The most common triggers are:

• Wrong password or username – especially after a recent password change on your email provider’s web portal.
• Outdated server settings – for example, using an old POP3/IMAP server name after your provider migrated to a new host.
• Authentication method mismatch – Outlook expects “Basic Authentication” but your provider now requires OAuth2 (common with Microsoft 365 and Gmail).
• Corrupted Outlook profile – the local data file or registry entries that store your account configuration may be damaged.
• Antivirus or firewall interference – security software occasionally blocks Outlook’s connection to the mail server.

Before You Start: Quick Checks

1. Confirm your email provider’s servers are not down (check their status page or try logging in via webmail).
2. Verify your internet connection works for other programs (browser, streaming, etc.).
3. Make sure your Outlook is updated to the latest version (File > Office Account > Update Options > Update Now).
4. If you recently changed your email password, update it in Outlook immediately.

Fix 1: Update Your Password in Outlook

The most common cause of 0x800ccc90 is an outdated password. When you change your email password on the provider’s website, Outlook continues using the old one until you update it.

1. Open Outlook and go to File > Account Settings > Account Settings.
2. Select your email account and click Change.
3. In the “Password” field, enter your new password.
4. Click Next and then Finish.

If you don’t know your current password, reset it via your provider’s webmail portal first. After resetting, repeat the steps above.

Fix 2: Verify Server Settings and Authentication

Incorrect server names or authentication methods are frequent culprits. Check your provider’s documentation for the exact incoming and outgoing server names, ports, and encryption methods. Common settings for IMAP and POP3 are:

• IMAP: port 993 with SSL/TLS (incoming), port 587 with STARTTLS (outgoing).
• POP3: port 995 with SSL/TLS (incoming), port 587 with STARTTLS (outgoing).
• SMTP: requires authentication – usually “Use same settings as my incoming mail server” or a dedicated SMTP login.

To check your current settings in Outlook:

1. Go to File > Account Settings > Account Settings.
2. Select your account and click Change.
3. Click More Settings > Advanced tab.
4. Verify the incoming and outgoing server names, ports, and encryption methods match your provider’s requirements.
5. On the Outgoing Server tab, ensure “My outgoing server (SMTP) requires authentication” is checked.

If you’re unsure about the correct values, search your provider’s help pages for “IMAP settings” or “POP3 settings”.

Fix 3: Rebuild Your Outlook Profile

A corrupted profile can cause authentication failures even with correct credentials. Rebuilding the profile is a reliable fix that preserves your emails (they remain on the server or in the OST file).

1. Close Outlook.
2. Open the Control Panel and search for Mail (or Mail (32-bit)).
3. Click Show Profiles.
4. Click Add to create a new profile, give it a name, and set up your email account with the correct settings.
5. Once created, select Always use this profile and choose the new profile from the drop-down.
6. Open Outlook with the new profile. If it connects successfully, you can delete the old profile later.

If you prefer to keep your existing profile, you can try repairing it via File > Account Settings > Repair (available in some versions). However, a fresh profile is often more effective.

Fix 4: Disable Antivirus or Firewall Temporarily

Security software can block Outlook’s connection to the mail server, especially after an update. To test this, temporarily disable your antivirus real-time protection and Windows Firewall, then try sending/receiving in Outlook. If it works, add Outlook as an exception in your security software. Remember to re-enable protection immediately after testing.

Fix 5: Use the Microsoft Support and Recovery Assistant

For Windows users, Microsoft offers a free tool called Microsoft Support and Recovery Assistant (SaRA). It can automatically diagnose and fix Outlook connection and authentication issues. Download it from Microsoft’s official website, run it, select “Outlook” and then “I’m having trouble with Outlook”, and follow the prompts. This tool is particularly useful for Microsoft 365 accounts.

When All Else Fails: Advanced Options

If the error persists, consider these less common but possible causes:

• Two-factor authentication (2FA): If you enabled 2FA, you may need to create an “app password” for Outlook instead of using your regular password.
• OAuth2 requirement: Some providers (Microsoft, Google) now require OAuth2 for Outlook connections. In Account Settings > Change > More Settings > Advanced, look for an “Authentication” or “Logon” option and select “OAuth2” if available.
• Corrupted Outlook data file: Run the Inbox Repair Tool (scanpst.exe) on your PST/OST file. Locate it in the Outlook installation folder (e.g., C:\Program Files\Microsoft Office\root\Office16).
• Registry issues: Rarely, a corrupted registry key for Outlook profiles can cause this error. This requires advanced troubleshooting – consider using a registry cleaner or contacting Microsoft support.

Frequently Asked Questions

Does error 0x800ccc90 mean my email account is hacked?

No, it simply means Outlook cannot authenticate with the server. It does not indicate a security breach. However, if you suspect unauthorized access, change your password immediately and check your account’s recent activity.

Will I lose my emails if I rebuild my Outlook profile?

No, your emails remain on the server (IMAP) or in the OST file (Exchange). When you set up the new profile, Outlook will synchronize your mailbox again. For POP3 accounts, your existing emails are stored in a PST file – you can reattach that file to the new profile.

Why does the error only happen on one computer?

If other devices connect fine, the issue is local to that computer – often a stale password cache, incorrect server settings, or interference from local security software. Rebuilding the profile usually resolves it.

Can I fix this error on Outlook for Mac?

Yes, the same principles apply. On Outlook for Mac, go to Tools > Accounts, select your account, and update the password or server settings. If that fails, delete the account and re-add it.

How do I know if my server uses IMAP or POP3?

Check your provider’s help page or look at your current Outlook settings (Account Settings > Change). If you’re unsure, IMAP is recommended because it syncs folders across devices and keeps emails on the server.

Is there a way to prevent this error from happening again?

Keep your Outlook updated, update your password in Outlook whenever you change it online, and avoid using weak passwords that might be changed by security policies. Also, ensure your antivirus software doesn’t block Outlook and periodically verify your server settings with your provider.

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