gmail said it received from a yahoo.com server. The yahoo.com is SHA Authed, so its probably genuine.
Which would mean that the
Received: from [80.87.84.30] by web35905.mail.mud.yahoo.com via HTTP; Tue, 23 May 2006 11:48:56 PDT
Header is genuine too because it was made by yahoo.
So the mail account most likely is
[email protected] and actually owned by the person that sent the mail, which was definately sent from 80.87.84.30 in that case.