[Prudence]

I have my own theory on the non-spam factor.

It's my totally unsupported by fact opinion that most free accounts sell subscriber email info to marketers. Which would explain how I can create an account and have spam in it before even telling anyone the address.

It is likewise my totally unsupported by fact opinion that gmail acts as a middle man advertising filter. Rather than sell your address blindly, they mine your email for relevant content and match that up with advertising on their end -- and bill the advertisers. Or some variation.

So you get marketed to either way, but one way is targeted (benefits advertisers) and doesn't involve selling your account address (benefits customers.)

Again, I have no facts to support these theories. And I recall reading an article where some hotmail exec swore they didn't sell addresses. But I don't believe them for a second.