Each message can have various labels assigned to it as a means
of classification. Each label has a name; different names are
different labels. Any given label is either present or absent on
a particular message. A few label names have standard meanings
and are given to messages automatically by Rmail when
appropriate; these special labels are called attributes. (See
Rmail Attributes.) All other labels are assigned only by users.
The a ( rmail-add-label) and k rmail-kill-label) commands allow
you to assign or remove any label on the current message. If the
label argument is empty, it means to assign or remove the same
label most recently assigned or Once you have given messages
labels to classify them as you wish, there are three ways to use
the labels: in moving, in summaries, and in sorting. C-M-n
labels <RET> rmail-next-labeled-message) moves to the next
message that has one of the labels labels. The argument labels
specifies one or more label names, separated by commas. C-M-p
rmail-previous-labeled-message