In the figure below, $R$ represents routers, ES$-$Ethernet switch.

a$.$ On PC$4,$ the e$-$mail application is communicating with the organization's e$-$Mail Server.

i$.$ At PC$4,$ name a protocol $($do not use abbreviations$)$ that may be used for each of layers $5,4,3$ and $2(5$ points$)$

ii$.$ What is the name the message at layers $5,4,3,2$ and $1$ of PC$4?(5$ points$)$