Read RFC $5321$ for SMTP$.$

$($a$)$ What does MTA stand for?

From $-$ Fri Nov $0713$:$41$:$302008$ Return$-$Path: Received: from barmail.cs$.$umass.edu $($barmail$.$cs$.$umass. edu $[128\mathrm{.}119\mathrm{.}240\mathrm{.}3])$ by cs$.$umass.edu $(8\mathrm{.}13\mathrm{.}1/8\mathrm{.}12\mathrm{.}6)$ for ; Fri, $7$ Nov $200813$:$27$:$10-0500$ Received: from asusus$-4$b$96($localhost $[127\mathrm{.}0\mathrm{.}0\mathrm{.}1])$ by barmail.cs$.$umass.edu $($Spam Firewall$)$ for ; Fri, $7$ Nov $200813$:$27$:$07-0500($EST$)$ Received: from asusus$-4$b$96([58\mathrm{.}88\mathrm{.}21\mathrm{.}177])$ by barmail. cs$.$umass.edu for ; Fri, $07$ Nov $200813$:$27$:$07-0500($EST$)$ Received: from $[58\mathrm{.}88\mathrm{.}21\mathrm{.}177]$ by inbnd$55.$exchangeddd. com; Sat, $8$ Nov $200801$:$27$:$07+0700$ From: $$Jonny$$ To: $$ Subject: How to secure your savings

$($b$)$ Assuming only the originator of this spam e$-$mail is malicious and all other hosts are honest, identify the malicious$$host that has generated this spam e$-$mail.