So when composing an email, you should keep a few points in mind.
First, some issues that are unique to email as opposed to an old fashioned letter.
The date is not necessary since the email will automatically be dated by the system. The address of the person you are sending it to is usually left off since you are emailing to a specific person. An email should contain an appropriate salutation such as 'Dear William:'. A signature line at the bottom should contain your name, company, business address, and phone number. This can be programmed to automatically be applied to every email you send. The notations section of a letter is unnecessary in an email. If you are copying someone that would be indicated in your email header. If you have an enclosure, the attachment would show in the email header.
Now some issues that are relevant to any letter including emails.
The tone of the salutation e.g. Dear William, and closing e.g. Yours Sincerely, should be appropriate to the relationship you have with the receiver of the email.
The body of the email should be kept as short as possible. Try to keep it to three paragraphs or about one minute of reading time if possible.
The email should address only one major topic. Each sub topic should be addressed in a separate paragraph.
The first paragraph should either get the reader's attention or preview what is to be discussed.
The last paragraph should either be a call to action or a summary of what was discussed.
The middle paragraphs should discuss the details of the topic. Include benefits, advantages, disadvantages, statistics, quotations or anything material to what you are trying to convey.