Why does Mail.app crash after macOS Sequoia 15.5?
Short answer: Sequoia 15.5 updated Mail's internal message-indexing engine. Mailboxes with large accumulated histories — especially accounts synced via iCloud Mail or Exchange — can land with a partially migrated index that crashes the app. Third-party Mail plugins (GPGMail for encrypted email, MailButler for tracking, SigPro for signatures) compiled against the 15.4 framework break immediately after the point update. Either cause is fixable in under 15 minutes.
How to fix Mail.app crash on macOS Sequoia 15.5
Step 1: Rebuild the mailbox index
Open Mail. If it launches without crashing, go to Mailbox in the menu bar and select Rebuild. Mail will re-index all messages from the server — this removes the corrupted local index file and rebuilds it cleanly. Rebuilding resolves the crash in the majority of Sequoia 15.5 Mail reports. Allow 10–30 minutes for large mailboxes. Do not close Mail during the rebuild. For multiple accounts, Mail may need to rebuild each account separately — repeat the process if needed.
Step 2: Launch Mail in plugin-safe mode to bypass crashes
If Mail crashes before you can reach the menu bar, hold the Option key and click the Mail icon in Finder (not in the Dock). Option-launching temporarily disables all Mail plugins and extensions. If Mail opens in this mode, a plugin is the cause. Navigate to Mailbox → Rebuild while in safe mode, then proceed to Step 3 to remove the offending plugin permanently.
Step 3: Remove third-party Mail plugins
In Finder, press Command+Shift+G and navigate to ~/Library/Mail/Bundles/. Move everything in that folder to the Trash. Also check ~/Library/Application Support/Mail/ for plugin-related folders. Restart your Mac and open Mail normally. This single step resolves plugin-caused crashes after every major macOS update. Once Mail runs stably, reinstall only the plugins you actually use — and check each plugin developer's website to confirm Sequoia 15.5 compatibility before reinstalling.
Step 4: The India angle — interrupted iCloud sync during update
In India, broadband connections — particularly on BSNL, ACT Fibernet, and some Jio Home Fiber plans — can experience brief drops during the macOS update download window. If iCloud was actively syncing your mailbox when the 15.5 update applied its Mail framework changes, the sync can leave partial envelope index files (Mail's local database of message headers) in an invalid state. The symptom is a crash specifically when Mail tries to load a particular folder or account. The fix is the same rebuild in Step 1, but if the rebuild itself fails, delete the ~/Library/Mail/V10/ folder (the current Sequoia envelope index path) entirely — Mail will recreate it fresh from server. Back up this folder first with Time Machine or a manual copy to the Desktop.
When to call a laptop repair service
When DIY ends
If rebuilding, removing plugins, and deleting the envelope index all fail to fix the crash, the underlying cause may be macOS system file corruption — not Mail-specific. At this point, a targeted macOS reinstall via Recovery Mode (Command+R on Intel Mac, hold the power button on Apple Silicon) reinstalls the OS without erasing your data and often resolves persistent app crashes. See our guide on macOS Recovery Mode issues if you need help with that process.
Typical repair cost in India
A macOS software service — OS reinstall, mailbox repair, data-safe fix — typically runs ₹800–₹1,500 at a reputable service centre. If SSD health is suspect (S.M.A.R.T. errors causing index corruption), SSD replacement starts from ₹2,000 for a quality NVMe drive, or our team can assess the drive health in a ₹149 doorstep visit.
A note from the LRW Engineer Team
Mail plugin conflicts after macOS updates are one of the most predictable and most preventable software issues we see. Before any major macOS update, open Mail → Preferences → Extensions and disable all third-party plugins. Update, verify Mail works, then re-enable plugins one at a time. This five-minute pre-update habit has saved many customers a post-update scramble. For Apple MacBook servicing or any macOS software repair, our team covers all Hyderabad zones.