Generally, each email program can be set to use a couple of different methods. We have to request that person to resend using the encoding method that we can decode. Lot's of websites out there that go into all the details. This can be avoided by using email software that automatically detects that messages arriving in your mailbox have an attachment.
Some people are real paranoid about the Internet.
That's the old self-centered nature we have and that'll probably be around for ever. The bulk of us just forget. Forgive them just like they will forgive you when you forget. Don't waste your time in anger and bitterness because life is just plain too short. Just as a matter of courtesy, start getting used to the idea of putting your name and email address at the end of your message so people will know who sent it and how to get back to you.