By right clicking on the incoming email you can generally see the return proxy by going into the details tab as well as the email alias for the sender's account. To give you one example of that,
Received: from 208.97.230.23 ([172.18.12.133])
by vms049.mailsrvcs.net (Sun Java System Messaging Server 6.2-4.02 (built Sep
9 2005)) with ESMTP id <
[email protected]> for
[email protected]; Fri, 15 Sep 2006 13:21:30 -0500 (CDT)
Received: from serv23.wolverinestatetelecom.com (208.97.230.23)
by sv17pub.nosuchplace.net (MailPass SMTP server w3.2.7 - 7312035152201RY+PrW)
with ESMTP id <5-15682-163-15682-62-1-1158346021> for vms049pub.nosuchplace.net;
Fri, 15 Sep 2006 13:47:01 -0500
Received: by serv23.wolverinestatetelecom.com id h1bmdm0boi4j; Fri,
15 Sep 2006 11:11:38 -0700
Date: Fri, 15 Sep 2006 13:21:29 -0500 (CDT)
Date-warning: Date header was inserted by vms049.mailsrvcs.net
From: <
[email protected]>
Subject: We'll fund your grant in 36hrs
X-Originating-IP: [208.97.230.23] (some typical spam now blocked)
This was done in Outlook since no yahoo mail here. Sorry about that. Generally when going to an inbox online for a proprietary account not a free mail type the return address is seen in the details.
If you are the sender then you are subject to the same things as far as return address and IP along with it. If you are just browsing and want to be invisible there are IP Blockers available to try out as well as some freewares available.