When you send a message while logged into the web version of GMail
with a from address other than the one you're logged into, GMail adds
a header tag "Sender" to prevent your message from being marked as
Spam by reputable spam systems.
When a Microsoft e-mail client reads the header, they use the MS
Exchange tag of "Sender" to create the "On Behalf Of" quasi-header.
It does this even if you're not using MS Exchange, and even though MS
Exchange isn't using the header the way it was defined to be used.
As Vijay mentioned, there are a couple ways to get around this... If
you use a POP/SMTP client to send, your client will generate the
headers so there will be no "Sender" header; but you run the risk of
being identified as Spam by receivers since you'll come from GMail
servers without a GMail address.
You can also sign up your alternate address in Google Apps for Your
Domain, provided you own the domain, and send from there. You can
search Google (or this forum) for information about GAfYD.
I was looking for a great spam filter for my personal domain email addy and
read about gmail's amazing filtering.
I have had my email service (about $9/yr) where my domain is hosted
(www.oneworlddomains.com) for several years. Their service is great, but
the spam filter is not that good.
Originally, I set-up gmail as my incoming and outgoing server and set-up
gmail to always send email from my private domain address, not my gmail
address. With those settings I was getting the "on behalf of" in the header
and bounce notices with "relaying not allowed" messages and outgoing
messages that disappeared into oblivion.
Then, I set-up outlook so my incoming server is gmail and my outgoing server
is my private address service. I haven't had any problems since.
And the gmail spam filter is amazing! I only log in once or twice a week to
check the spam folder to see if anything was marked incorrectly. I have
been doing if for a month now and there have been a few, but it is 1000
times better than what I had before.
Jenna