To save the current mail message to a file:
& s junk
This saves the current mail message to the file junk in the current directory.
To save several mail messages to the same file:
& s 5 8 14 project/feedback
This saves messages 5, 8 and 14 to the file feedback. This file is in the the subdirectory tmp of the directory from which the mail program is being run.
To save all the messages from a particular user:
& s cayman xgator
This saves all the messages with the string cayman in the From: field of their message header to the file xgator.