---
id: mac-storage-basics.what-does-rebuild-mailbox-do
url: https://storagestudio.us/faq/mac-storage-basics/what-does-rebuild-mailbox-do
category: "Mac storage basics"
subcategory: "Mail, Messages and chat apps"
question: "What does Rebuild do in Apple Mail, and does it free space?"
alt_questions:
  - "mailbox rebuild mac"
  - "rebuild mail index"
  - "mail rebuild mailbox storage"
  - "mail showing wrong messages fix"
short_answer: "It re-reads the selected mailbox and rebuilds its index to fix missing or garbled messages. It isn't a cleanup tool and may re-download mail."
tags: ["mail", "rebuild", "troubleshooting"]
related: ["https://storagestudio.us/faq/mac-storage-basics/why-is-apple-mail-using-so-much-space"]
applies_to: "all"
last_reviewed: 2026-10-01
---

# What does Rebuild do in Apple Mail, and does it free space?

**Mailbox → Rebuild** re-reads the selected mailbox from the server (or disk) and rebuilds Mail's index of it. It fixes missing or garbled messages and wrong counts.

It isn't a space-saving tool: for IMAP accounts, Mail downloads the mailbox again, which can temporarily use more space and time. Use it to fix problems, not to clean up.