Four parts of an E-mail

Subject line In emails subject line is compulsory, its purpose is to summarize the main idea. It is easy for busy readers to glance at a subject line to quickly decide whether to read the message or not. 

Opening-Most emails and memos open direct by the purpose should be restated and amplified in the first sentence. 

Body Only one topic is discussed through good emails. The body provides the reasons for writing.

Closing The closing should include action information dates and deadlines. A summary of main points may be an appropriate closing.

Guffey, M; Rhodes, K; Rogin, P; Business Communication Process and Product. Canada 6th Ed, 2011 page 222