rfc2822 April 2001

4.4. Obsolete Addressing

   There are three primary differences in addressing.  First, mailbox
   addresses were allowed to have a route portion before the addr-spec
   when enclosed in "<" and ">".  The route is simply a comma-separated
   list of domain names, each preceded by "@", and the list terminated
   by a colon.  Second, CFWS were allowed between the period-separated
   elements of local-part and domain (i.e., dot-atom was not used).  In
   addition, local-part is allowed to contain quoted-string in addition
   to just atom.  Finally, mailbox-list and address-list were allowed to
   have "null" members.  That is, there could be two or more commas in
   such a list with nothing in between them.

obs-angle-addr  =       [CFWS] "<" [obs-route] addr-spec ">" [CFWS]

obs-route       =       [CFWS] obs-domain-list ":" [CFWS]

obs-domain-list =       "@" domain *(*(CFWS / "," ) [CFWS] "@" domain)

obs-local-part  =       word *("." word)

obs-domain      =       atom *("." atom)

obs-mbox-list   =       1*([mailbox] [CFWS] "," [CFWS]) [mailbox]

obs-addr-list   =       1*([address] [CFWS] "," [CFWS]) [address]

   When interpreting addresses, the route portion SHOULD be ignored.