Internal Memo features:

• accuracy about incident
• keeping in mind that you might not be able to be totally forthcoming
• clear plan
• describes problem and solution clearly
  
• content
• broken into chunks (headers if appropriate)
• use of bullets
• use of text decoration
  
• audience
• for employees or a subset of employees
• relevance 
• What's this mean to me?
  
• format
• header
• opening
  
• summary
• discussion
• closing
• appended relevant documents
• Feel or tone
  
• length
• person usage
• establishes relationship between sender/receiver
• Mechanics