Some labels such as deleted and filed have built-in meanings, and Rmail assigns them to messages automatically at appropriate times; these labels are called attributes. Here is a list of Rmail attributes:

unseen

Means the message has never been current. Assigned to messages when they come from an inbox file, and removed when a message is made current. When you start Rmail, it initially shows the first message that has this attribute.

deleted

Means the message is deleted. Assigned by deletion commands and removed by undeletion commands (Rmail Deletion).

filed

Means the message has been copied to some other file. Assigned by the o and C-o file output commands (Rmail Output).

answered

Means you have mailed an answer to the message. Assigned by the r command (rmail-reply). Rmail Reply.

forwarded

Means you have forwarded the message. Assigned by the f command (rmail-forward). Rmail Reply.

edited

Means you have edited the text of the message within Rmail. Rmail Editing.

resent

Means you have resent the message. Assigned by the command M-x rmail-resend. Rmail Reply.

retried

Means you have retried a failed outgoing message. Assigned by the command M-x rmail-retry-failure. Rmail Reply.

All other labels are assigned or removed only by users, and have no standard meaning.