telnet port 25
Oh the joys of telneting to port 25 and sending people emails. We did this a fair amount at uni. You could even use the "mail from" to put in a lecturer's email address so that it looked like the email came from a lecturer. My favourite use of smtp was the following:

When we were in Senior honours the new Junior Honours were a bit wet behind the ears and were being slagged somewhat by the SH, this prompted the following email to be sent from the head of computer science to all the Senior honours students:

From [email protected].***.ac.uk Wed May 23 14:31:40 2001
Date: Thu, 23 Sep 1999 14:53:09 +0100 (BST)
From: Ron Morrison

It has come to my attention that all the SH have been being rather nasty to the
new JH. If I catch anyone sending any more derogatory emails about the JH, even on the spods mailing list. I will have to suspend their accounts and report them to the hebdomadar. After all it is not the junior Honours fault that they are fucking wankers.
yours,
Ron Morison
(thrain, Thu 14 Jan 2010, 17:29, 2 replies)

Knowing DCS,
one can probably still do this :)
(Fawksie, Thu 14 Jan 2010, 20:04, closed)

I did something like that.
Mine went to the whole university, and made the student newspaper.
( idonthaveafunnynickname Drink-Aware? Sure. I'm aware I want another drink., Fri 15 Jan 2010, 0:43, closed)