Now both email and snail mail is in use. I personally prefer using email, due to the following reasons,
1) Email is much cheaper than snail mail, meaning that it is used for many more purposes. For example, you didn't see a lot of jokes forwarded to you in the post.
2) Email is obviously much faster than snail mail. This means that exchanges can happen more quickly and the writing has become a lot more conversational as a result. Now you don't need to pack a month's information into a letter since you can just exchange multiple emails.
3) Email can be to groups. While a letter can be copied and sent to multiple people, it rarely resulted in the kind of group exchange that email can with mailing lists, reply all and other such technical features that facilitate collaboration