Give these definitions, how do we know how good our spam filter is performing? How do we compare each other in an apples-to-apples comparison?
Another defining characteristic of spam is volume; if it's not in bulk, it's not spam. Defining "bulk" is challenging, of course.
The distinction between unsolicited and now-unwanted email is an important one.
I have for years defined spam as bulk, unsolicited email with commercial intent. I'm starting to wonder whether the "commercial intent" qualifier is reasonable. A charity or political party that sends bulk, unsolicited email promoting itself should probably also be viewed as spamming.
Perhaps "unsolicited email, in bulk" is now definition enough.
<i>"if it's not in bulk, it's not spam"</i>
I disagree. Even a single message can be spam. Spam is what the end users defines as spam, and the end user has no knowledge on the bulkiness of the message (or even the timespan over which it is distributed so as not to look as a bulk message).
uh oh, we're falling at the first gate ;)
We in SpamAssassin-land define spam as UBE -- bulk, not necessarily commercial. If I get religious spam or political spam, it's still spam despite being uncommercial -- it's the fact that it was sent in bulk to millions of recipients that makes it spammy.
I think UBE is an easier definition than UCE, to be honest.
I agree that there are multiple ways to define spam. Unsolicted Bulk/Commercial Email is the simplest way. Or, to paraphrase my own definition, bulk mail that the average person would not expect to want to receive.
While there is some ambiguity in this definition, this shouldn't be construed as a problem. In the legal system, people are to be found guilty beyond a reasonable doubt. What constitutes reasonable? It's ambiguous but not an obstacle to conviction.