By Doug Lowe

As a network administrator, part of your job is protecting your users from spam. But, what is spam? The most basic definition of spam is any email that arrives in your inbox that you didn’t ask for. Spam is unsolicited email.

It’s email that isn’t welcome, email that you aren’t expecting. It’s email from people you don’t know or haven’t heard of, usually trying to sell you something you aren’t interested in or couldn’t possibly need, and often trying to trick you into parting with either your money or your valuable personal information, or both.

One of the defining characteristics of spam is that it’s sent out in bulk, often to thousands or even millions of recipients all at once. Most spam is not particularly well targeted. Instead of taking the time to figure out who might be interested in a particular product, spammers find it easier and cheaper to pitch their products to every email address they can get their hands on.

Spam is often compared to junk mail of the physical kind — the brochures, catalogs, and other solicitations that show up in your mailbox every day. In fact, spam is often called “junk email.”

However, there is a crucial difference between physical junk mail and junk email. With physical junk mail, the sender must pay the cost of postage. As a result, even though junk mail can be annoying, most junk mail is carefully targeted. Junk mailers don’t want to waste their money on postage to send mail to people who aren’t interested in what they have to sell. They carefully measure response rates to ensure that their mailings are profitable.

In contrast, it costs very little money to send huge numbers of emails. To be sure, spam is expensive. But the bulk of the cost of spam is borne by the recipients, who must spend time and money to receive, store, and manage the unwelcome email, and by the network providers, who must build out their networks with ever greater capacity and speed to accommodate the huge volumes of spam emails that their networks must carry.

Estimates vary, but most studies indicate that as much as three-quarters of all the email sent via the Internet is spam. At the time that I wrote this, there were indications that spam was actually becoming less common, accounting for closer to half of all the emails sent. But some organizations report that 80 percent or 90 percent of the email that they receive is actually spam.

One thing is sure: Spam is not just annoying; it’s dangerous. Besides filling up your users’ inboxes with unwanted email, spam emails often carry attachments that harbor viruses or other malware, or entice your users into clicking links that take them to websites that can infect your network. If your network is ever taken down by a virus, there’s a very good chance that the virus entered your network by way of spam.

So, understanding spam and taking precautions to block it are an important part of any network administrator’s job.