Gregory's Server
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.