Review questions 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?