Messages, Mail and chat attachments: the space on your Mac you forgot about

A Mac that has been signed in to the same Apple Account for a few years carries every photo, video, voice note and PDF anyone has sent it. Messages keeps them forever by default. Mail keeps them for as long as the email exists. Chat apps keep their own copies. Then you saved the important ones to Downloads, so many of them are on the disk twice.

This can easily run to tens of gigabytes, and it is spread across folders most people never open. Here is where it lives and how to remove it without breaking anything.

First, the setting that decides what "delete" means

Open Messages › Settings › iMessage and look at Enable Messages in iCloud.

• If it is on, your conversations sync across your devices. Deleting an attachment on your Mac deletes it on your iPhone and iPad too. That is fine if you want it gone everywhere, and a bad surprise if you only wanted space back on the Mac.
• If it is off, deletions on the Mac stay on the Mac.

Decide which you want before going on. If your phone is the place you keep everything, the Mac-only route below is the safer one.

Messages

Messages stores attachments in ~/Library/Messages/Attachments. Do not delete from that folder in Finder. Messages still refers to the files, and your conversations will show broken attachments. Use one of these instead.

See and remove the largest attachments. Open System Settings › General › Storage, and click the ⓘ beside Messages. You get a list of attachments sorted by size, with conversations, photos, videos and other files listed separately. Select the ones you do not need and press Delete.

Stop keeping everything forever. In Messages › Settings › General, change Keep messages from Forever to 1 Year or 30 Days. Older conversations and their attachments are deleted, permanently, so save anything you care about first. With Messages in iCloud on, this applies to all your devices.

Clear one conversation. In the conversation, choose View › Show Details or click the name at the top, scroll to Photos or Files, and delete from there.

Mail

Mail keeps each message, with its attachments, in ~/Library/Mail. There are two easy wins and one that takes a little longer.

• The Mail Downloads folder. When you open an attachment, Mail copies it to ~/Library/Containers/com.apple.mail/Data/Library/Mail Downloads. The originals are still in the emails, so this folder is safe to empty. Quit Mail first.
• Download Attachments. For an IMAP account, Mail › Settings › Accounts › Account Information has a Download Attachments menu. Setting it to Recent or None stops Mail storing every attachment locally. They are fetched from the server when you open them.
• Delete the large emails themselves. On the server, this frees space in your mailbox and, through syncing, on your Mac. Most webmail services can search by size, for example larger:10M in Gmail.

Chat apps

WhatsApp, Telegram, Slack and similar apps keep their own copies of everything sent to you, in folders inside ~/Library/Containers or ~/Library/Group Containers named after the app. As with Messages, delete from inside the app, not from Finder. Most have a storage section in their settings that lists the largest chats and media and lets you clear them. Where one does not, open the chat's shared media and delete from there.

The copies you saved

Every attachment you dragged out of a conversation or an email is now a separate file, usually in Downloads, often under a name like IMG_4021 (2).jpeg. These do not belong to any app, so you can remove them freely. They are also easy to forget, because the original is still in the conversation.

Sort Downloads by size in Finder (View › as List, then click the Size column), and look out for videos and anything with a number in brackets in its name.

Doing it with SweepyMac

SweepyMac does not delete anything from inside Messages, Mail or chat apps, and it should not. Those apps keep track of their own attachments, and removing the files underneath them is how you end up with broken conversations. What SweepyMac does is show you where the space is and clean up the copies that belong to nobody.

• Space Lens draws any folder as a map of bubbles sized by space used. Point it at your Library folder and you can see at once whether Messages, Mail or a chat app's container is the large one, before you open each app's settings. Its job here is to point you to the right app.
• Large & Old finds big, old files in a folder you choose, such as Downloads, with a minimum size from 10 MB and an age. It skips your Library folders on purpose, so it will not offer files Messages and Mail are still using.
• Duplicates finds byte-identical files, including the attachment you saved three times. It keeps the oldest copy of each set and pre-selects the rest. Finding duplicate files explains how it decides.

Everything goes to the Trash first, with Undo. SweepyMac needs Full Disk Access to measure folders like Messages, which macOS protects. Full Disk Access, explained covers why and what it does with it.

SweepyMac has a three-day free trial with no account, then from $14.99 a year or $59.96 once. Download it from its page.