"Save Changes" Runs Out of Disk Space

If you try to save changes, by selecting Save Changes or Done from the File menu, or by switching mail folders, and Mail Tool warns that it has run out of disk space, you must remove messages from the current mail file to make it small enough to save.

You can remove messages by deleting or moving them. Removing larger messages helps the most. You can find the largest messages by choosing Size from the Sort By submenu of the View menu.