The highest number of spam mail received by a single person is Microsoft founder Bill Gates, according to Steve Ballmer. Bill Gates receives four million e-mails per year, out of which most are spam. The estimated cost in monetary view spent on spamming annually is $21.58 billion as per the 2004 survey.

So, how can the spam mails be stopped or atleast stopped from reaching the inboxes?

One method employed involves using a white list of email addresses. For example, the owner of the email account can set the server to only allow emails from senders that are in the owner’s addressbook. This is often used in combination with methods to give new senders an opportunity to request inclusion in the owner’s addressbook. For example:
1. All email originating from senders not in the addressbook are sent an automatic response stating that their email has not reached the recipient (ie. the email account owner).
2. The sender is given the option of sending the recipient an addressbook inclusion request via an online form.
3. The online form includes a captcha to only allow requests from human (non-computer-automated) sources.
4. If the recipient (account owner) approves the request, current and future email from the sender reaches the recipient with no further filtering.
Yahoo dropped a similar feature from their webmail service in 2005.

Anti-spam techniques should not be employed on abuse@ email addresses, as is commonly the case. The result of this is that when people attempt to report spam to a host, the spam message is caught in the spam filter and the host remains unaware that their network is being exploited by spammers.

But, how do the spammers know my e-mail address?

The answer is Email harvesting.

In order to send spam, spammers need to obtain the e-mail addresses of the intended recipients. To this end, both spammers themselves and list merchants gather huge lists of potential e-mail addresses. Since spam is, by definition, unsolicited, this address harvesting is done without the consent (and sometimes against the expressed will) of the address owners. As a consequence, spammers’ address lists are inaccurate. A single spam run may target tens of millions of possible addresses — many of which are invalid, malformed, or undeliverable.

Sometimes, if the sent spam is “bounced” or sent back to the sender by various programs that eliminate spam, or if the recipient clicks on an unsubscribe link, that may cause that email address to be marked as “valid”, which is interpreted by the spammer as “send me more”.

Hmm, What does spam mail mostly consist of?

As per the study posted by Wikipedia: