Sites like Google, Outlook, Yahoo, and social sites like Facebook, Linkedin, or Twitter can detect if you are creating many accounts from the same computer.
They do that by 2 main techniques:
Tracking your IP address: You can see your find your IP address on sites like this.
Tracking your Browser Fingerprint: You can see your browser fingerprint on sites like this.
Some websites may use some more advanced tracking, like keyboard biometrics. You can test such a fingerprint on sites like this.
Most of the websites look at the reputation of your IP, and how warmed your browser too.
This seminar is a step-by-step guide to resolving all these problems.
When to Follow this Seminar?
Based on our experience, email providers like Gmail are very permissive about creating up to 5-7 Google accounts from the same IP, with no issues. Social sites like Facebook and LinkedIn are much more restrictive.
You should apply this seminar if you are planning to scale outside these boundaries.