how do companies know so many email ids to send bulk mails?

Answer 1

There are many ways where such companies 'harvest' email addresses:

- through other companies that offer to sell their client e-mail addresses (often you see such disclosures when you sign up for services which you could choose not to let you address be passed to a third party)

- programs that crawl the web (possibly making use of search engines as well) that harvest e-mail addresses from personal websites (in pages that have the 'mailto' tag which follows an e-mail address).

- blogs, where people list their contact details (e-mail addresses)

- Viruses, Worms that infect computers and copy all the addresses in the address book and send them to a specific computer (the spammer's possibly)

- From other companies that do not have secure customer data protection policies. Some critical systems are misconfigured, or the data is viewable to the world from outside. In such cases, spammers expoit this.

These are some of the common ways where companies harvest e-mail addresses.

Answer 2

the companies do it with computer's help. once you send your email add to any company... it will automatically recognise your id and auto send bulk mails. it doesnt send bulk mails without your first visit.

Answer 3

Spammers buy email address lists from numerous sources, they scan places like Usenet, webpages, etc. for any likely email address (they look for the @), even by just "guessing" with a computer program that generates millions of possible combinations that will probably yield hundreds of legitimate addresses.

Answer 4

Sometimes when you give your e-mail address to a company, they sell it to another company that will constantly spam you. It's a shame :(