Mail Not Working After macOS Upgrade? Fix It

If your Mail app breaks or misbehaves right after a macOS upgrade, the fix is usually a combination of restarting Mail, checking your internet connection, and re-entering your email password. This guide walks you through the most common causes and the exact steps to get Mail working again, from simple restarts to rebuilding your mailbox.

Why macOS Upgrades Break Mail

Mail is tightly integrated with the operating system, so a major macOS update can disrupt it in several ways. The upgrade process itself can leave behind corrupted preference files, outdated account credentials, or a half-finished migration of your mailbox data. Apple also changes how Mail handles certain email providers and security protocols between versions, which can cause accounts that worked before to suddenly fail. Finally, the upgrade may reset network settings or permissions that Mail depends on, leading to connection errors or crashes.

Start With the Basics: Restart and Check Connections

Before diving into deeper fixes, try these quick steps. They resolve a surprising number of post-upgrade Mail problems.

1. Quit and reopen Mail. Press Cmd+Q to fully quit Mail, then reopen it from the Dock or Applications folder.
2. Restart your Mac. A full restart clears temporary system glitches that the upgrade may have left behind.
3. Check your internet connection. Open a web browser and load a site. If that fails, restart your Wi-Fi or router.
4. Check Apple’s System Status page. If iCloud Mail is down, no local fix will help. Visit apple.com/support/systemstatus to confirm.

Re-Enter Your Email Password

After an upgrade, Mail often loses the stored password for your email account, especially for non-iCloud providers like Gmail, Yahoo, or Outlook. This shows up as a “Cannot connect to the server” error or a password prompt that reappears endlessly.

1. Open System Settings (or System Preferences on older macOS) and click Internet Accounts.
2. Select the email account that’s failing.
3. Click Account Details or the account name, then re-enter your password.
4. If you use two-factor authentication, you may need to generate an app-specific password from your email provider’s website and use that instead of your regular password.
5. Click OK and then check Mail again.

Delete and Re-Add the Account

If re-entering the password doesn’t work, remove the account from Mail and add it back. This forces Mail to rebuild its connection settings from scratch, which often clears up upgrade-related corruption.

1. In Mail, go to Mail > Settings (or Preferences) and click the Accounts tab.
2. Select the problem account and click the minus ( – ) button to remove it. Choose to keep or delete the mailbox data on your Mac—keeping it is safer.
3. Click the plus ( + ) button and re-add the account. Enter your email address and password, and let Mail auto-configure the settings.
4. If auto-configuration fails, you’ll need to enter the incoming and outgoing server details manually. These are available from your email provider’s help page.

Rebuild Your Mailbox

If Mail opens but shows old messages missing, or crashes when you click a specific folder, the mailbox index may be corrupted. Rebuilding forces Mail to re-download and re-index messages from the server.

1. In Mail, select the mailbox (Inbox, Sent, etc.) that’s causing trouble.
2. Go to Mailbox > Rebuild in the menu bar.
3. Wait for the process to finish. It can take a while if you have a large mailbox, and Mail may appear unresponsive during this time.
4. If the problem persists, try the same for all mailboxes under the account.

Reset Mail’s Preferences (When Nothing Else Works)

Corrupted preference files are a classic post-upgrade culprit. Resetting them restores Mail to default settings, but you’ll lose custom signatures, rules, and layout choices. Your emails themselves are not deleted.

1. Quit Mail completely.
2. Open Finder and press Cmd+Shift+G, then type ~/Library/Preferences/ and press Enter.
3. Find files that start with com.apple.mail (for example, com.apple.mail.plist). Move them to the Desktop or Trash.
4. Reopen Mail. It will create new preference files and ask you to set up your accounts again.
5. If Mail still crashes, also delete the folder ~/Library/Containers/com.apple.mail/Data/Library/Preferences/—but back it up first, as it contains some account data.

Common Post-Upgrade Mail Problems and Their Specific Fixes

Here are the most frequently reported issues after a macOS upgrade, each with a targeted solution:

• Mail won’t open at all. Try launching it while holding the Shift key to prevent windows from restoring. If that fails, reset preferences as above.
• Mail opens but crashes when you click a message. This is often a corrupted message in the inbox. Rebuild the mailbox, and if that doesn’t work, move the suspect message to a different folder or delete it from the server via webmail.
• New emails don’t arrive, but you can send. Check your incoming server settings (usually IMAP or POP). Go to Settings > Accounts > Account Details > Server Settings and verify the server name and port match your provider’s documentation.
• Emails are duplicated. This happens when the mailbox index is out of sync. Rebuild the mailbox, and if duplicates persist, remove the account and re-add it.
• Mail uses too much CPU or battery. This often follows a large migration. Rebuild the affected mailbox, then restart your Mac. If it continues, check for a stuck message in your Outbox and delete it.

Frequently Asked Questions

Will I lose my emails if I remove the account from Mail?

No. Removing an account from Mail only disconnects it from the app. Your emails remain on the server (if you use IMAP) or on your Mac (if you use POP and chose to keep local copies). When you re-add the account, messages will reappear.

Why does Mail keep asking for my password after the upgrade?

macOS upgrades often invalidate stored credentials, especially if your email provider changed its security requirements. Re-enter the password in System Settings > Internet Accounts. If you use two-factor authentication, you may need an app-specific password from your provider.

Can I downgrade macOS to fix Mail?

Yes, but it’s a drastic step. You would need to erase your Mac and reinstall the previous version from a backup or a bootable installer. Only do this if you’ve exhausted all other fixes and have a complete backup, as it’s time-consuming and can cause other issues.

Why does Mail work on my iPhone but not on my Mac?

Each device stores its own account settings and credentials. The Mac’s settings may have been corrupted during the upgrade, while the iPhone’s were untouched. Follow the steps to re-enter your password or re-add the account on the Mac.

What if Mail still doesn’t work after trying everything?

Create a new user account on your Mac and test Mail there. If it works, the problem is specific to your user folder. If it doesn’t, the issue is system-wide. In either case, contact Apple Support or your email provider’s support for further help, as they may have specific guidance for your configuration.

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