What does the word "Ham" mean in this context?

Probably everybody knows these days what ["Spam"] means in the context of e-mail. The use of the word Ham on the other side is relatively new and sometimes confusing.

"Ham" is e-mail that is not ["Spam"], more or less the "good" mail. Previously it was often called non-spam or solicited mail. Because these words are both a bit long-winded, somebody came up with the catchy word Ham.

Editorial notes:

• Can somebody please wordsmith this text a bit?
• Who was it who first introduced the word Ham, does somebody have a link?
  

Thanks, MalteStretz

I gave it a quick touch-up, but it isn't polished yet.
SidneyMarkowitz