Fix macOS Monterey Mail app crashing on launch

Quick answer (for the impatient)

Hold Option while opening Mail. This forces a database rebuild. If that doesn't work, delete the Envelope Index files manually (instructions below).

Why this happens

Monterey's Mail app is a bit of a disaster when it comes to database corruption. The Envelope Index file — the database that holds message metadata — gets corrupted after a crash, a failed update, or just random disk issues. I see this most often after someone force-quits Mail while it's still indexing a large mailbox, or after a macOS update that didn't go cleanly. The app tries to load the index, hits a bad entry, and immediately crashes. No error message, no warning — just a bounce in the dock and then nothing.

The good news: you almost never need to reinstall macOS or wipe your mail accounts. The index files are replaceable. Your actual emails live on the server (or in the raw mbox files), so rebuilding the index just forces Mail to re-read them.

Step-by-step fix: Rebuild the Envelope Index

Quit Mail completely. Right-click the Mail icon in the Dock, choose Quit. Or press Cmd+Q. Make sure it's not running — check Activity Monitor if you're paranoid.
Open the Mail folder in Finder. Click the desktop, then from the menu bar: Go > Go to Folder. Type
```
~/Library/Mail/V10/
```
and press Return. The V10 folder contains Monterey's Mail data. (V9 is for Big Sur, V8 for Catalina — if you upgraded from an older version, check those too.)
Find the MailData folder. Inside V10, look for a folder named MailData. It's usually right there. If you have multiple accounts, you might have an Accounts subfolder — skip that. The MailData folder is the one with the index files.
Move these files to your Desktop (or Trash):
- Envelope Index
- Envelope Index-shm
- Envelope Index-wal
Don't delete them yet — just in case. Drag them to your Desktop. If you don't see a file with -shm or -wal, that's fine. The main Envelope Index file is the critical one.
Open Mail again. Double-click the Mail icon. It will launch, but it'll be slow — Mail will rebuild the entire index from scratch. Depending on how many emails you have, this could take 5–15 minutes. The status bar at the bottom will show "Importing messages..." or "Updating mailbox...". Let it finish.
Test it. After the rebuild finishes, close Mail and reopen it. If it opens without crashing, you're golden. If it still crashes, move on to the alternative fixes below.

Alternative fix: Safe mode and reindex

If the manual index rebuild didn't work, try booting into Safe Mode. This clears system caches that might be conflicting with Mail.

Shut down your Mac.
Turn it on and immediately hold the Shift key until you see the login screen. You'll see "Safe Boot" in the top-right corner.
Log in. Wait for the desktop to load (it'll be slower than usual).
Open Mail. If it opens in Safe Mode, close it and restart normally. Then try Mail again.
If Mail still won't open in Safe Mode, the problem isn't just a cache issue. Move on to the next section.

If all else fails: Create a new Mail account

Sometimes the account configuration itself gets corrupted. This is rare, but I've seen it on Monterey after a bad iCloud sync.

Go to System Preferences > Internet Accounts.
Select your email account (iCloud, Gmail, whatever).
Click the minus button to remove it. Important: Check "Delete from Mac" but uncheck "Delete from iCloud" if it's your iCloud account — otherwise you'll wipe your server-side mail.
Re-add the account: click the plus button, choose the service, enter credentials.
Open Mail. It'll rebuild the index from scratch for that account.

Prevention tip: Keep your mailbox compacted

Once Mail is working, go to Mailbox > Rebuild. Do this once a month if you have large mailboxes (10,000+ messages). It's like defragmenting a hard drive — it keeps the index tidy and less prone to corruption. Also, never force-quit Mail while it's doing a mailbox operation (like moving 500 messages). Wait for the spinning gear to stop. That single habit has saved me more headaches than any software update.

One last thing: If you're on Monterey 12.3 or later, there's a known bug with Exchange accounts that causes crashes on launch. If you have an Exchange account (work/school), try removing that account first using the steps above. Apple never officially fixed it, but rebuilding the index works 9 times out of 10.