I am thankful for the way the Internet has made it easier for us to communicate. Our own organization not only uses e-mail extensively but is also constantly looking for new ways to use the Internet to bring the Gospel to those who do not know Christ.
But I suspect many people would echo your complaint; it's become far too easy to waste time on the Internet, as you've discovered. One solution, of course, would be for you to delete e-mails you know are useless, without reading them. That will take discipline, of course, but you shouldn't feel compelled to read an e-mail just because someone sent it to you.
After all, you probably don't read every word in your newspaper or watch every program on television. Neither should you bother reading every e-mail, if you know you'll only be wasting time. Another option might be to send out a general e-mail, telling people that your e-mail has become so time-consuming that you'll no longer be able to read forwarded e-mails.
Behind your question is an important spiritual truth: Every minute is a gift from God, and we shouldn't waste even one of them. The Bible says, "Make the most of every opportunity" (Colossians 4:5). Put your life into Christ's hands, and then ask Him to help you use your time in ways that honor Him.