Subaddresses provide a convenient handle for screening e-mail
    messages with DELIVER.

    To screen mail based upon a subaddress, you must use a 1, 2,
    or 3 action to obtain the envelope TO: address associated with
    the mail message being delivered to you. You cannot use headers
    since there is no requirement that your address has to appear in
    the header of messages you receive, either with or without the
    subaddress. For instance, to detect the subaddress "junk-mail",
    use the directives

    *  *             * T 2 "ENVELOPE-TO"
    * "*+junk-mail*" * T D WASTEBASKET

    The first of these two directives tells DELIVER to use the
    envelope TO: address for 2-PATTERN. The second directive then
    causes any messages with +junk-mail appearing in the envelope TO:
    address to be filed to your WASTEBASKET folder.