Which element is only found in an email and not in friendly or business letters? body salutation signature subject line

subject line

Explanation:

A subject line is the introduction that identifies the emails intent. This subject line, displayed to the email user or recipient when they look at their list of messages in their inbox, should tell the recipient what the message is about, what the sender wants to convey.

In both of the email and friendly/business letters, when you are done with what you have said, the signature goes at the bottom, signing you off.

They both have the salutations and the body. The body deals with what the email and or letter is addressing completely and such. The salutations are used for greetings and such.