You can reduce the amount of space taken up by the Mail app by moving or deleting messages with large attachments to your “Trash” folder. First, consider finding out how much disk space is being used by Mail, so you can compare after: 1. Launch Finder. 2. Long-press the “Option” key. 3. Select “Go,” “Library” then right-click the Mail folder. 4. Choose “Get Info.” There you’ll see the size and space used. To move emails to another mailbox: 1. Launch Mail. 2. Select the message[s] you wish to move. 3. Next, either drag the message[s] to another mailbox via the sidebar or the “Favorites” bar. 4. Alternatively, select the “Move to” option via the toolbar. If you have already downloaded the email attachments, then you can remove them from the messages. To remove large messages no longer in use: 1. Select the message you wish to remove the attachment from. 2. Choose “Remove Attachments.” This way the message can remain in your mailbox without taking up as much space. Next, delete your Trash folder as Mail will still occupy space from the Trash: 1. Launch Mail. 2. From the menu bar, choose “Mailbox.” 3. Choose “Erase Deleted Items.” 4. Select a mailbox option from the context menu: “In All Accounts” or “On My Mac.” 5. Select “Erase” in the confirmation dialog box.