foldername

    Indicates the name of the folder to which the current message
    is to be 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 to be moved. If you omit the file name, Mail moves the message
    to the specified folder in the current file.