How to Free Up Space Taken by Mail on Mac (Attachments Are the Culprit)

In Apple's storage screen there's a line that drives people nuts: Mail — 8 GB. And the maddening part is you open the Mail app, look around, and it feels empty. You don't have 8 GB of email. Your inbox has maybe two hundred messages.

The 8 GB isn't the text of your emails. It's everything ever attached to them — every PDF, invoice, screenshot, and 40 MB "here's the deck" someone emailed you since 2016. Mail keeps a local copy of all of it, forever, by default. Here's how to claw that back.

Why Mail storage is bigger than it looks

A plain-text email is basically free — a few KB. The problem is attachments, and two behaviors that compound them:

• Every recipient keeps a full copy. If you're on a thread where someone emailed a 25 MB file to twelve people, that's 25 MB on each of your machines, not shared.
• Deleting the message doesn't always delete the blob. Mail stores attachments in a shared store; the message is just a pointer. Old "deleted" mail in the archive, plus that giant attachment still referenced, is where the mystery gigabytes live.

So the fix isn't "delete more emails." It's find the big attachments and remove them (or the mailboxes holding them).

Step 1: see what Mail is actually holding

Before deleting anything, get the number. Two quick ways:

Sort by size inside Mail. Open a mailbox, then in the message list use View → Sort By → Size. The top of the list is almost always attachment-heavy messages. Delete the ones you don't need, then empty the Trash mailbox in Mail (this matters — Mail's trash isn't the system Trash, and it still counts until emptied).

Look at the raw folder. Mail's data lives in ~/Library/Mail/ — Finder → Go → hold Option → Library → Mail. Inside, the V*/ folder (V3, V4, V5 depending on macOS version) holds the actual message and attachment store, and you can see its real size. This is view only for most people — don't start hand-deleting files in here, Mail's database tracks them and corrupting that link is how you break the app.

The point of looking is to confirm the size, not to go surgery-happy in the folder.

Step 2: the safe, high-leverage moves

Ordered by "biggest win, least risk":

• Empty Mail's own Trash and Junk mailboxes. The single most forgotten step. Right-click each in the sidebar → Empty. Old deleted mail with attachments is often a chunk of the total.
• Delete large old attachments you've saved elsewhere. Sort by size, and for each big one: if you already have the file in Downloads or Drive, delete the email. You're not losing it, you're removing the duplicate copy Mail kept.
• Archive or delete whole old mailboxes you never read. Work inboxes from jobs you left, notification-mail folders, that "Photos from 2018" thread.
• Turn off local download for accounts you don't need offline. In Mail → Settings → Accounts → Mailbox Properties, set messages to download "recent" rather than all, so old attachment-heavy mail stays on the server and off your disk.

What you should not do: delete files directly inside ~/Library/Mail to "make room." You'll desync Mail's index and spend your afternoon rebuilding it.

Step 3: the version that doesn't make you do all that

If "sort, judge, and empty four mailboxes" sounds like exactly the kind of fiddly, low-confidence task you'd rather not do, this is a good place to stop doing it manually.

The Mail Attachments cleanup in CleanDiskGo scans the Mail store, lists attachments by size with the message they came from, and lets you clear the big old ones without you poking around in ~/Library/Mail hoping you didn't break the database. It's the same logic as the manual steps — find the fat attachments, remove them — just with the risky folder-browsing taken out of it.

Worth flagging the distinction: this is about the Mail app. If your storage is being eaten by iMessage pictures and videos instead, that's a completely different pile of files — I cover that separately in how to delete iMessage attachments on Mac. People routinely confuse the two because both show up as "messages" in their head, but they live in different places and clean up differently.

How much this is actually worth

Mail can genuinely be several gigabytes on a machine that's been used for work for years — it's one of the more reliably bloated apps precisely because nobody ever prunes it. But it's a bounded win: you clear the old attachments, set the download policy, and it stops being a problem for a long while.

If Mail's a few GB and your disk's still full, it's not the main event, and I'd point you at the bigger levers instead: what's actually taking up your space, and what that "System Data" number is really made of. But if that storage line says "Mail: 8 GB" and you've never once looked at it — start here. It's an easy win hiding in plain sight.