foldername

    Indicates the name of the folder to which the current message is
    moved. If the specified folder does not exist, Mail asks whether
    you want to create it. If you respond with Y, Mail creates the
    new folder.

    A folder name can be 1 to 39 characters in length. Valid
    characters for folder names are alphanumeric characters, dollar
    signs ($), and underscores (_). If your folder name contains
    lowercase letters, spaces or special characters, the folder name
    must be enclosed in quotation marks.

 file-spec

    Indicates the name of the mail file to which the current message
    is moved. If the specified file does not exist, Mail creates
    it. If the file name is omitted, Mail moves the message to the
    specified folder in the current file.