Is it illegal if i extracted thousands of emails, available publicly, from a popular site and sold it to someone?
I got an offer from one person and I don’t know if i should do it.
Yeah I got my answer. Thanks guys for your time.
I had doubts about doing it so I asked here. Now I know it is not such a good idea.
Whether or not it's illegal it's certainly morally wrong. If someone is willing to pay for a list of email addresses then they're planning to do something which will generate revenue in some way. Whether that's sending spam or phishing emails it still means you're causing a headache for innocent people.
Even if I do not go by the above issues, probably this guy is more interested in the email IDs available for bulk email marketing or spamming, depending on the perspective, which maybe totally unwanted for the email ID owners.
As you have not given us much detail, it's difficult to give you an accurate answer, but here are some issues to consider.
Jan says correctly the fact that something is available to the public to read does not mean there's no copyright on it. Copyright is the right to control who should have access to the material and and to allow (or not allow) copies being made. So on the copyright front, you will need to check the what terms that "popular website" gives. If they don't, then in terms of the law, you would have to write to them and ask for permission to copy. There is no legal argument against that (except as details below).
Secondly, it depends on the emails themselves. Are they copyrighted? For example, if they were written by private individuals, then they are also subject to copyright, unless they were specifically and explicitly put in the public domain (and by that I don't mean that they are available publicly, but that the authors stated that they are in the public domain, which is essentially "with no copyright").
Depending on the context and the content, you may also find yourself accused of breaching people's privacy, state secrets or promoting terrorism... Without having any idea what these emails are, it's difficult to tell.
On the other hand, there are two defences you can use in law regarding those breaches. One is "fair use" which is essentially that you are only copying a small amount of the material and it's for your own use (study etc). This defence is available in the US, but not in all other countries (for example, there is no such concept in the UK). The second is that making the emails available to others is in the public interest. This tends to be used by journalists who have either obtained materials illegally (by paying someone who stole them, or by hacking into a system) or by releasing them without permission. Again, legislation differs from one country to the next, but many countries do allow such a defence. I don't think either of these would really work for you.
In short, if the scenario is that you are offering, essentially a "packaging service" by downloading and distributing material which is publicly available, you need to check with the copyright holders (site, authors etc). If circulating the material in itself can be contentious, take legal advice first, or better yet, don't do it!
Depends on the basis the emails were made available (copyright license).
In general you are not allowed to copy and especially sell content from a public website, be it emails, articles, images or whatever. All of it is intellectual property.