each question 4 to 5 lines 

• 8.1 What is the difference between RFC 5321 and RFC 5322?
• 8.2 What are the SMTP and MIME standards?
• 8.3 What is the difference between a MIME content type and a MIME transfer encoding?
• 8.4 Briefly explain base64 encoding.
• 8.5 Why is base64 conversion useful for an e-mail application?
• 8.6 What is S/MIME?
• 8.7 What are the four principal services provided by S/MIME?
• 8.8 What is the utility of a detached signature?
• 8.9 What is DKIM?