It's not a problem according to how email works but can confound those that didn't know.
My wife has an ASUS K52F Notebook with Intel I5 2.67GHz processor and 4GB memory. She has Windows 7 Home Premium OS and uses Outlook 2010 as her mail client.
She recently wanted to reply to a friend's email and selected the Reply option, however, a completely unknown email address appeared in the address box. I checked the Properties of the email and found that this unknown address also appeared in the "Delivery Options" box. She contacted her friend who reported that someone else had experienced the same problem with one of her emails with the same reply address appearing.
While the problem appears to be in my wife's friend's system, I would like to know what might be causing it.
The linked article did nothing to explain the issue. It appears to relate to organisations with subscriber lists, which my wife is not. Perhaps someone might have a direct answer as to why a strange address, not the sender's, is appearing in a Reply box for an email sent by an individual to an individual.
Light bulbs you shouldn't buy
There are plenty of dimmable LED light bulbs, but make sure you don't buy the ones that flicker when you dial them down.