"Mail receiver server"

[manatlan]

In an intranet/lan, i'd like to put a "python server script" (which run 
forever) on a computer A...

On another computer B, I'd like to send smtp-email to the computer A ... 
(send to "user at 126.52.12.12", for example ...126.52.12.12 is the ip 
address of "B")

in fact, i'd like to control "computer A" by sending smtp email from 
"computer B".

What kind of server should i write on computer "B", a smtp server ? a 
pop server ?
(i think i have to make a script which listen on a port, and execute 
some handlers ... but i don't know how to start)

i know python very well, but i dont know anything about smtp/lan
if you have a recipe to build this kind of server, it could be good
but i'm pretty sure it can be easy to do ...