When I was young, I used to send back attached .doc or .xls files with
the excuse that I don't use Microsoft products on my computer, which
wasn't even a PC. I pissed off many people by telling them that
sending Microsoft formatted files is not politically correct and it is
also rude to make assumptions about the recipient's computer system.

Now I just open them with openoffice (or whatever else will open them)
and don't even blink an eye.

It's funny how time changes things.

On the yahoo/blacksheep question, I am subscribed to both as there are
emails on both that are worth reading. I don't like yahoo, google and
the rest but here I am, using a gmail address and admitting it works
fine, after I realised how unreliable my ISP delivering mail. A
practical or lazy solution has won over a more ethical  one.

73, Dimitris VK1SV