If you have been sending letters to people or to your customers for many years, you cannot stop doing it suddenly. I can think of many advantages of sending letters comparing to sending emails. Letters are more personal than emails. If you send a letter to somebody, you are guaranteed that this person will not miss this letter. Having said that, emails are easy to ignore by their recipients. Those who send many letters can familiarize themselves with custom envelope printing to make their letters even more enjoyable to look at. Custom envelope printing allows senders make their letters more attractive.