While working with a client today, I uncovered a handy tip that could save you an extremely large amount of hard drive space on your Mac. My client had just purchased a new 13-inch MacBook Pro and had her information transferred from her old machine.
Shortly thereafter she began receiving error messages that her startup disk was full and that she needed to delete files on her machine in order to continue using it.
The first place I looked for extraneous files was in media folders. Typically, deleting video and high-resolution photo files will give the quickest relief to a lack of hard disk space. Unfortunately, my client did not have these files on her machine, so we had to look elsewhere.
Upon inspecting Mail, I noticed that a few folders named "Recovered Messages" had over 1,500 unread messages sitting in them. My client informed me that this folder had appeared and continued to fill itself with a single e-mail.
The message was over 27Mb and continued to copy itself from the Gmail server back to her Mac. Even after deleting the folder, Mail recreated it and continued downloading the message from Gmail.
To solve the situation, I opened the Mail Preferences (Command + , ) and chose the offending Gmail account. I clicked on the Advanced tab and changed the "Keep a Copy for Offline viewing" setting below:
Since the Gmail account was being accessed via IMAP, there is no need to keep a copy of your messages for offline viewing as they will always be in sync each time you access your account from Mail. These saved messages, once deleted from my client's Mac, saved her nearly 200GB of hard-drive space.