Gmail is great in that you can add other email addresses to your inbox and receive email sent to those addresses and reply from those addresses.
The problem has been that when you reply from an address that isn’t your Gmail, Google has added an “on behalf of” to the message.
I understand they have done this mostly because they really have to because of Mail delivery protocols etc.
It kind of irked me because, if I want to send from another address, I want to do it right.
Well, Google recently implemented a change (thanks to Public feedback) in that, to comply with protocol, email ‘sent from’ will be sent from the server where the address the email is being sent on behalf of instead of from the Gmail servers.
At least that’s how I understand it.
More at the Official Gmail Blog