If you have multiple email accounts, you can direct incoming mail of each account into a different mail folder. You can also use mail filters to direct incoming mail based on several criteria. Finally you can move messages into mail folders manually. Email groups are useful when you are continually sending email to a group of people. Everyone who was sent the original email will be included in the group.
Mail is listed by the order it arrives, by default.
Clicking on the column heading in the folder window sorts the messages by that field. You can tell how the mail is sorted because you will see a small arrow next to the column heading. Clicking on this arrow will resort the messages in the opposite order. When messages are deleted, they are moved to the trash. You must empty the trash to free up this disk space.