SMTPSVC(5.0.2195.5600)
Received:
X-Message-Info:
Message-ID:
X-Priority:
X-MSMail-Priority
X-Mailer:
X-MimeOLE:
Importance:
In-Reply-To:
Return-Path:
X-OriginalArrivalTime

Some are obvious, but this is always in the head of hotmail emails.

ta

Si

 

From memory, the headers prefixed with X-* are MTA specific extensions, and are only of interest to the source MTA.

The rest are standard headers which you'd find in RFC821, or one of its subsequent derivations.

Google it if you want to know more.