为什么电子邮件会取代传统邮寄？

The reason why traditional postage mails is replaced by emails is because the latter one is on time and less time-consuming instantaneous and free. If we rely on posting, it takes a couple of days for the recipients to receive the letters Thus they have now termed as "snail mail". What is worse, if the sender and recipient reside in different countries, it would take much longer for the delivery of the words. This is especially so when the sender and receipient reside in far away countries.  In contrary sending email saves the time and ensures the recipients can read the content on a timely basis. Furthermore, the in-advanced preparation of sending a letter by post is complex. For example, it is necessary to have letter paper and pen ready. When the letter is finished, we need to purchase stamps and seek for post box to get it sent. Based on the above factors, the number of people relying on traditional postage is decreasing dramatically. On the other hand, emails don't require preparatory work, that is looking for a piece of paper, then a pen, after finishing it, one still has to go to the post office to buy stamps, if you don't have any at home, look for a parking spot and wait in line at the post office.  Of course there is the long wait to see if your mail has been received by the other end!  Sure, email also needs preparatory work too, just turn on the computer and get into your email software. When you are done, just press a button and voila!

How could not anyone use email given these reasons?  Snail mail will become dead as a doornail as the younger generations inherit the earth.

你的英文語法沒錯, 不过, 写得太繁文縟節了因為理由又重復又太直接明顯. 要用不同的方向来表達才是有意思.