Rebuild a Mailbox in Mac Mail to Fix Missing or Duplicate Emails

Published ✓ Verified ⏱️ 2 min read August 23, 2025 · by Ryan Bennett

Some messages look missing, garbled, or duplicated in a mailbox in the Mail app on your Mac, even though they’re fine on the web.

Why: Mail keeps a local copy of each mailbox. If that local copy gets out of step with the server, messages show up wrong. Rebuilding throws away the local copy and re-downloads the mailbox fresh from the server.

Fix 1: Rebuild the affected mailbox

In the Mail sidebar, click the mailbox that has the problem (for example the inbox for one account).
Choose Mailbox > Rebuild.
The mailbox may look empty for a while — that’s expected. Wait for Mail to finish re-downloading before judging the result.

For IMAP or Exchange accounts, the messages and attachments stored on your Mac are discarded and then downloaded again from the server, so the mailbox appears empty until the download is complete.

Fix 2: Make sure the account is online first

Rebuilding only works if Mail can reach the server.

Choose Mailbox > Take All Accounts Online so the account isn’t offline (no lightning bolt in the sidebar).
Confirm your Mac has a working internet connection.
Then run the rebuild in Fix 1.

Fix 3: Rebuild each mailbox that looks wrong

A rebuild applies to the one mailbox you have selected, not the whole account.

Repeat Fix 1 for any other mailbox that shows missing, garbled, or duplicate messages — for example a Sent or Archive folder.
Give each one time to finish re-downloading before moving to the next.

FAQ

Will I lose my email by rebuilding? No — for IMAP and Exchange accounts the messages live on the server and are downloaded again. Only the local copy on your Mac is discarded and refreshed.

Why does the mailbox go empty during a rebuild? Because the local copy is cleared first, then re-downloaded. It fills back in as the download completes; don’t quit Mail mid-rebuild.

When should I rebuild? When messages appear missing or garbled, or when searching with the Entire Message option doesn’t find messages you know are there.

Sources: Apple Support — Rebuild mailboxes in Mail on Mac, Apple Support — If you can’t see email messages in Mail on Mac