the purpose of the letter is

You have it on record, what you have actually expressed. This is of course particularly true, when you use the e-mail system as your medium. Usually the time and place is simultaneously recorded as well
.What has been said by whom to whom where and when may easily be forgottenThe receiver also has on record, what you have expressed, as well as any additional information concerning the letter.You can take your time, when you compose a letter, making sure, that there is no chance of ambiguity, that the grammar and the spelling is impeccable, and that the factual content is absolutely correct.In case the letter is written on paper it is possible to end the letter with a hand-written signature to guarantee the authenticity of the letter.Letters can in some cases be used as evidence in a court of law, whereas it is far more difficult to establish, what has been said orally by whom and when to whom either directly or over the phone.In hand written letters it may in some cases be easier to express deep emotions and keep passionate contact with loved ones far away than by talking over the phone, which might also be either impossible, difficult or very expensive.