Mail downloads and attachments: how much space Mail really uses

Part of: Mac storage full? Find what is using it and free up space safely (Storage full)

Mail stores your messages and their attachments on your Mac so that you can read them offline. Over the years, that can become many gigabytes. To reduce it safely, work from inside Mail and be sure which copy of a message is the only one.

Check how big it is

Run this in Terminal. It only reads:

du -sh ~/Library/Mail

The size depends on how many accounts you have and how much mail is kept offline. On some Macs the number is small, for example when mail is mostly kept on a server. Terminal may need Full Disk Access to read this folder, and a small number can mean it was not allowed to look.

What is inside

• Messages and mailboxes. Your mail, kept for offline reading.
• Attachments. Files that came with messages. These are usually the bulk.
• Opened attachments. Copies of attachments you opened from a message may be kept separately from the mailbox.

Know where your mail really lives

Before you remove anything, answer one question: if I delete this from my Mac, does a copy remain on the mail server? With IMAP-style accounts, such as most Gmail, iCloud and work accounts, the server keeps the messages and your Mac keeps a copy. With an older POP-style account, the Mac may hold the only copy.

If you are not sure which type you have, assume the Mac holds the only copy and do not delete.

Safe, Risky, Never

• Safe: removing copies of attachments that are still on the server, or attachments you saved elsewhere and checked.
• Risky: deleting messages or mailboxes. If the server does not keep a copy, they are gone for good.
• Never: deleting folders inside ~/Library/Mail by hand. Mail keeps a database of its messages, and removing files behind its back can leave it inconsistent and make mail appear missing.

What breaks if you get it wrong: messages or attachments disappear, search stops working properly, or Mail has to rebuild its data and re-download mail, which can take a long time.

How to reduce it safely

1. Delete in Mail, not in Finder. Mail updates its own records when you do.
2. Look for large messages. Sorting by size in a mailbox shows the biggest attachments. Delete the ones you do not need.
3. Save what matters first. Drag an important attachment to a folder of your own, and check that it opens, before you delete the message.
4. Check how the account is set up. The account settings in Mail let you control how much is kept offline. The exact options depend on the account and the macOS version, so this guide does not give a click path.
5. Empty the Trash. Deleted mail still uses space until it is gone. The same idea as with files: see why moving files to the Trash does not free up space.

A different place to look

If the Mail folder is small but your Library is large, look elsewhere. Why is the Library folder so big? walks through the biggest subfolders. Chat attachments are covered in Messages attachments taking up space.

If you want to keep a message but free the space

You do not have to choose between keeping an old message and freeing space. For messages with large attachments, you can save the attachment to a folder of your own and delete the attachment from the message, if Mail offers that for your account. Check that the saved copy opens before you remove anything.

For an entire old mailbox you still want, a different option is to export it somewhere safe, such as an external drive, and then clear it from the Mac. Exporting makes a copy first, so the original removal is a smaller risk. The exact steps depend on your account and your macOS version, so read what Mail offers in its own menus before you begin. Take your time here. Email is often a record of important things, and a careful approach costs only a little patience.

See what is big

DiskJoy is our product. It scans the folders you allow and shows large items with sizes and an explanation. A scan only reads file sizes and dates and changes nothing. DiskJoy is pre-alpha and cleanup is not available yet, so you remove things yourself, and you should not need it to touch your mail. Download DiskJoy for Mac if you want the sizes in one place.

Next step

Back to the complete guide to freeing up space on a Mac.