6.1. SYNTAX

     address     =  mailbox                      ; one addressee
                 /  group                        ; named list

     group       =  phrase ":" [#mailbox] ";"

     mailbox     =  addr-spec                    ; simple address
                 /  phrase route-addr            ; name & addr-spec

     route-addr  =  "<" [route] addr-spec ">"

     route       =  1#("@" domain) ":"           ; path-relative

     addr-spec   =  local-part "@" domain        ; global address

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

     domain      =  sub-domain *("." sub-domain)

     sub-domain  =  domain-ref / domain-literal

     domain-ref  =  atom                         ; symbolic reference