When considering the cost of roofing materials, many people take into account just the shingle prices. This is incorrect, as a roof made just of roofing shingles will not work. You also need to consider all the accessories that are included in a complete roof system.
The differences between emails and letters is that, emails are send electronically and arrives faster to the person that you are sending it too, while in the other hand letters takes a little bit longer to arrives to the person and can be lost from the mailing company especially whens sending it overseas also it cost money.
Stick to one topic in a business email and write only the things that are appropriate for anyone to read, as email forwarding makes it possible for originally unintended parties to receive the email. Proper grammar and spelling is very important in business emails because it reflects on you and your abilities.