Include only the relevant text of the original message, commenting where appropriate. Text written with the caps lock on means, in the email world, the sender is yelling. It may seem like a small point, but people are sensitive. Users should include the same information at the bottom of the email that would normally be included in a standard letter. For instance, name, title, and company name.
Email makes doing business easier.
It's nice to be able to answer mail at your own convenience or to put a quick question out on a listserve.