Some iPhone users report that Mail suddenly stops working, showing errors like “Connection to the server failed”, server code: AUTHENTICATIONFAILED, or SERVER MESSAGE: AUTHENTICATE INVALID CREDENTIALS.

Mail plays an essential role in our digital lives, and when it stops working, it can disrupt both work and personal communication. If you’re experiencing this issue on your iPhone, this guide will walk you through possible causes and solutions.

Possible Causes

Mail authentication errors usually occur for two main reasons:

1. New Device or Location Login

When you sign in to your email account on a different device, browser, or even from a different location, the email provider may flag it as a security event and temporarily reject the login until verified.

2. Email Providers Requiring App-Specific Passwords

Some email providers (like Yahoo, Microsoft Exchange, Google, AOL, Outlook, etc.) require a special app password (different from your regular email password) when using third-party email clients — including Apple’s Mail app.

In such cases, you’ll need to generate an app-specific password through your email provider’s website or account security settings and use that in place of your normal password when adding the account to your iPhone.

Solutions to Fix the Issue

1. Temporarily Turn Off the Email Account

You can disable the mail account in Settings and re-enable it later to refresh the connection.

• Go to Settings -> Mail -> Accounts. Tap the email account you want to disable.

• Toggle Mail off. If it’s an iCloud email account, toggle off Use on this iPhone.

After a few moments, turn it back on to see if the issue is resolved.

2. Remove and Re-add the Email Account

Sometimes removing and re-adding the account clears the issue.

• Go to Settings -> Mail -> Accounts. Select the account that’s having issues.

• Tap Delete Account (or Sign Out for iCloud).

To add the account back:

• Go to Settings -> Mail -> Accounts -> Add Account.

• Follow the prompts to sign in again, using the correct password or app-specific password if required.

3. Restart Your iPhone

If the problem persists, try restarting your iPhone.

• Go to Settings -> General -> Shut Down. Slide to power off.

• Once the device is fully off, press and hold the Side button until the Apple logo appears.

By following these steps, most Mail authentication issues on iPhone can be resolved. If none of these solutions work, check with your email provider to ensure there are no account-related security blocks or service outages affecting your login.

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