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 hand 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

Using 'ham' for non-SPAM mail is extremely irritating. It reminds of the word 'harm' so that everybody thinks of 'ham mail' as some new kind of SPAM in the first place. It shouldn't be used here or anywhere else.
lee