How to Reduce Mail Storage on Mac (Downloads & Rebuild)

In short: Apple Mail can quietly grow to tens of gigabytes as attachments and cached messages pile up. Here is how to reclaim that space safely by removing downloads and rebuilding mailboxes. Every step below keeps your actual email intact.

If your MacBook is running low on space, Apple Mail is often a bigger culprit than people expect. Over months and years, downloaded attachments and locally cached messages can quietly balloon into tens of gigabytes. The good news is that you can reduce Mail storage on Mac without losing a single email, as long as you work carefully and keep everything reversible.

This guide covers the two most effective moves: clearing out old attachment downloads and rebuilding your mailboxes so Mail resyncs a leaner local copy. These steps apply to macOS Sonoma (14) and Sequoia (15).

See how much space Mail is actually using

Before you change anything, get a real number. Open the Apple menu, choose System Settings, then General and Storage. Wait a moment for the categories to calculate, then look at Mail in the list. Clicking the small info icon next to it shows a breakdown you can review.

If you would rather see the folder directly, open Finder, press Command-Shift-G, and go to ~/Library/Mail. That is where Mail keeps its local database and downloaded attachments. Look, but do not start dragging things out by hand. Mail manages this folder itself, and the safe way to shrink it is through the app, which we will do below.

Clear old attachment downloads

Attachments are usually the largest single cause of a bloated Mail folder. When you open a message, Mail often downloads and caches the full attachment locally, even for mail that also lives on the server. Removing those local copies frees space, and because the originals stay on the server (for IMAP, iCloud, Gmail, and most Exchange accounts), you can always re-download them later.

To remove a single attachment, open the message in Mail, then choose Message in the menu bar and select Remove Attachments. The message text remains, and a small note shows the attachment was removed. To find the heaviest offenders quickly, click the Sort by control at the top of the message list and choose Size, so the biggest messages float to the top.

You can also change how much Mail stores going forward. Open Mail, then Settings, click Accounts, select your account, and open the Account Information tab. Under Download Attachments, switch from All to Recent or None. Mail will then keep fewer local copies and pull attachments on demand when you actually open them.

Rebuild a mailbox to reclaim wasted space

Over time, a mailbox database can hold onto space from deleted messages and stale indexes. Rebuilding tells Mail to discard its local cache for that mailbox and download a fresh, compact copy from the server. It is one of the most reliable ways to reduce Mail storage on Mac.

Select a mailbox in the sidebar, then choose Mailbox in the menu bar and click Rebuild. Depending on the mailbox size and your connection, this can take a few minutes and temporarily hide messages while it resyncs, so do it when you are online and not in a rush. Rebuild each large mailbox in turn rather than all at once, so you can watch the results.

Rebuild only works well for accounts that keep a server copy, such as iCloud, Gmail, or Exchange. For a POP account where the Mac holds the only copy, back up first, because those messages are not stored elsewhere.

Empty Trash and Junk, then restart Mail

Deleting messages does not always free space immediately, because Mail keeps them in per-account Trash and Junk mailboxes. Choose Mailbox, then Erase Deleted Items and Erase Junk Mail, and pick the account. You can also set Mail to purge automatically under Settings, Accounts, Mailbox Behaviors. After clearing, quit Mail completely with Command-Q and reopen it so the storage figures settle.

Keep it reversible and verify what is happening

A quick safety reminder: the reliable way to clean anything on a Mac is to preview first and send removals to the Trash, not to permanently delete them. That way a mistake is a quick restore, not a lost file. Stick to your own user-level data in ~/Library and never delete anything inside /System. Real email lives on the server for most accounts, so clearing local caches is low risk, but working reversibly keeps it that way.

If you would rather have a tool handle the wider cleanup around Mail, choose one that shows a preview before it touches anything, only clears user-level junk by default, and moves removals to the Trash. A cleaner has no reason to contact the internet, and you can confirm that yourself with a firewall like Little Snitch. On that basis, CoreSweep is our top free pick: free forever, an optional one-time Pro at $49, zero telemetry, and reversible Trash-based deletes. If you want something lighter, SkoonMac is the best-value runner-up, free with a one-time Pro at $19.

Work through these steps in order and you can typically recover several gigabytes from Mail alone, with every message still safely in place.

Frequently asked questions

Does removing Mail attachments or rebuilding a mailbox delete my emails?

No. Removing an attachment leaves the message text intact, and rebuilding tells Mail to download a fresh copy from the server. For IMAP, iCloud, Gmail, and most Exchange accounts the originals stay on the server, so you can re-download anything later. The exception is POP accounts, where the Mac holds the only copy, so back those up first.

Why is Apple Mail using so much storage on my Mac?

Over months and years, downloaded attachments and locally cached messages pile up in Mail's local database, which can quietly grow to tens of gigabytes. Cached attachments are usually the single largest cause. You can check the real number in System Settings under General and Storage, then look at the Mail entry.

Can I just delete the ~/Library/Mail folder to free space?

No, avoid dragging things out of that folder by hand. Mail manages ~/Library/Mail itself, and the safe way to shrink it is through the app by removing attachments, rebuilding mailboxes, and erasing Trash and Junk. Stick to reversible, in-app steps and send any removals to the Trash rather than deleting them permanently.

← All Mac cleaning guides · Back to the comparison