You can create files to organize your mail messages. You use
    the same commands to create a mail file that you use to create a
    folder: COPY, MOVE, and FILE. After Mail prompts you for the name
    of the folder, it also prompts you for a file name. If you enter
    a new file name at the File: prompt, a new mail file is created.

    For example, to move the current message into a folder named FEED
    in the ACCOUNTS file, enter the following commands:

    MAIL> MOVE
    _Folder:  FEED <Return>
    _File:  ACCOUNTS <Return>

    The MOVE command creates the mail file ACCOUNTS.MAI (if it does
    not already exist), moves the current message into the FEED
    folder, and deletes the message from its current folder and file.

    To work within a mail file other than the default file (usually
    a file called MAIL), use the command SET FILE to specify the
    alternate file. The command SHOW FILE displays the name of the
    current mail file. When you change mail files, Mail deletes the
    messages in the WASTEBASKET folder of the current mail file if
    AUTO_PURGE is set, and closes the mail file that you were using.