Dear Lazyweb, can anyone explain to me the conditions under which Outlook corrupts the "From" field by putting "On Behalf Of" into it?

Does it always copy Sender into there? Or Return-Path? Or is it doing something even more stupid?

E.g., an outgoing message, as received at Google, looks like this:

Return-Path: <A@gmail.com>
Received: from ... by mx.google.com ... TLSv1
Sender: A@gmail.com
From: Full Name <A@dnalounge.com>
X-Mailer: Apple Mail (2.2070.6)

And then when some schmuck who has the poor taste to be using Outlook hits reply, this is what comes back:

Delivered-To: A@gmail.com
Return-Path: <B@example.com>
Received: ... by mx.google.com ... for <A@gmail.com> ... TLSv1.2
Received-SPF: neutral ... neither permitted nor denied
Authentication-Results: ... spf=neutral
Received: ... TLSv1 for <A@dnalounge.com>
From: "Other Guy" <B@example.com>
To: "'Full Name'" <A@dnalounge.com>
X-Mailer: Microsoft Office Outlook 12.0

Herp derp I top-reply

-----Original Message-----
From: Full Name [mailto:A@gmail.com] On Behalf Of Full Name
Sent: Wednesday, March 04, 2015 9:01 PM
To: Other Guy

Herp derp I quote the entire message

Now I'm just an unfrozen caveman, your modern MICROS~1 ways frighten and confuse me, but one thing that I DO know is that presenting a mailto: link pointing at the contents of the Sender: header is complete insanity and I would like it to stop.

Previously.