Why is e-mail so popular over conventional mail ?

e-mail is popular over conventional mail because:

1. It is cheaper.
2. An e-mail is faster.
3. It saves paper and reduces waste.
4. It is easy to use.
5. A record is maintained of all the e-mails sent and received.
6. It is flexible as the recepient can respond at his convenience.
7. It is available 24 hours a day 7 days a week.