Gregory's Server
Back in 2001, when LinkedIn was in beta and i was working at a college, i got an email from one of my friends asking me to sign up to LinkedIn.
I said sure, and used the college email. After they extracted the contents of the address book that was attached to the college's email, everyone in the college received an email from the Dean, who had been targeted specifically.
All the staff at that college signed up.
"If the boss asks for it then..."
@briankrebs
A couple of years later, after Companies House in London created a web-portal to their database, they did a scrape of the email addresses of every company director, which gave them a second wave of sign-up's.
I know this because i used a #BlueDyeEmail address for the company i had registered.
At a techie meetup 6 months later, i was gossiping with a couple of software engineers who had worked for LinkedIn, who confirmed that the spamming was how LinkedIn got it's early customers.