How do I fix Mail Stuck “Indexing” / 100% CPU on macOS Tahoe 26.2?

Three approaches in order of safety: (1) Force Reindex of Envelope Index; (2) Clean the Mail Cache. Full Terminal commands and System Settings paths are inside each section.

Is this fix confirmed for macOS Tahoe 26.2?

Yes — verified on macOS Tahoe 26.2. Article is updated when Apple ships a point release that changes the symptom or fix.

How to Fix Mail Stuck “Indexing” / 100% CPU on macOS Tahoe 26.2

Symptom: The Mail app on macOS Tahoe 26.2 shows a "Downloading Messages" or "Indexing" progress bar that never completes, often consuming 100% of a CPU core for hours.

TL;DR fix

Quit Mail. In Terminal run rm ~/Library/Mail/V12/MailData/Envelope\ Index* (use V11 if you're on an older Mail data version). Reopen Mail and let it rebuild the index — the progress bar runs but completes this time. If CPU is still pinned, also clear ~/Library/Containers/com.apple.mail/Data/Library/Caches/*.

Why this happens

The Tahoe Mail database schema update can fail if there are orphaned attachments or corrupted V11/V12 folder structures.

Fix 1: Force Reindex of Envelope Index

Quit Mail.
In Finder, go to ~/Library/Mail/V11/MailData/ (or V12 in Tahoe).
Delete any files starting with "Envelope Index".

rm ~/Library/Mail/V12/MailData/Envelope\ Index*

Re-open Mail and wait for the reindex to complete.

Fix 2: Clean the Mail Cache

Open Terminal.
Run:

rm -rf ~/Library/Containers/com.apple.mail/Data/Library/Caches/*

Restart Mail.

Tested and documented by the MacDebug team — about MacDebug. See also Freeform Text Duplication Bug on Tahoe 26.2, Mac Wi-Fi Drops After Sleep on Tahoe 26.2, or browse all guides on macdebug.