Considering how many times over the years, I see blind people on different lists not know how to respond privately to someone, here are instructions that will work on some, perhaps many, e-mail programs.
Be on the message in the message list.
Open the message properties with alt enter, that is, hold alt and press enter.
Issue the command control tab.
Try down arrowing. If you can't down arrow, tab once. Now try down arrowing again. If you have to tab once, do that every time you follow this procedure before down arrowing.
Now start down arrowing through the message headers.
There will be a lot of information but you will find a line that says from and then gives the address of the sender.
Move to the start of the address.
Then use the command shift end to select it.
Copy it to the clipboard.
Close properties with escape.
Then start a new message and paste the address into the clipboard.
Some e-mail lists won't display the original sender's address in the properties or anywhere else but many lists do.
It would be a good idea if people would send instructions about how to reply privately with different e-mail programs. I know the method I gave works in Outlook Express, Windows Live Mail and, presumably Windows Mail. I don't know if it works in Word or Thunderbird.