address     =  mailbox                      ; one addressee
                 /  group                        ; named list
...
     mailbox     =  addr-spec                    ; simple address
                 /  phrase route-addr            ; name & addr-spec
...
     addr-spec   =  local-part "@" domain        ; global address

     local-part  =  word *("." word)             ; uninterpreted                                                 ; case-preserve