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Stopping junk mail is tough for a reason. Companies view virtually everything about you as a commodity to be sold or traded.

That includes your name and address, your age and an estimate of your income, the size of your mortgage and what you just bought on their websites or in their stores, and how much you spent there.

You may think the fact that you just purchased a swimsuit or a toy or a truss is your own bleeping business, but it's not. The retailer thinks your information is part of its business. It may share what it gleans about you with other retailers in huge databases known as co-ops that exist to help companies prospect for consumers. The retailer may sell your information to database brokers, who in turn sell it to other companies.

You don't have much of a say in this. Financial companies are required to send annual opt-out notices so customers can exclude themselves from all this sharing and trading. Other types of companies are not. There's no "don't trade me, bro" option to click when you're checking out.

That leads to an onslaught of marketers trying to grab your attention and mailboxes stuffed with junk. Many people try to fight back against this ambush. But some of the methods they try don't work. For instance, they:

Refuse to buy online. Sorry, but junk mail existed long before the Internet. Online purchases make it easy for retailers, who are prohibited from harvesting information from credit cards, to learn your address and other details about you. But companies have other methods of gleaning information, from loyalty cards to contest forms to magazine subscription databases. Public records provide a wealth of information about you as well. If you buy a home, get married, have a kid or file for bankruptcy, those events are recorded in public databases that are mined by marketers.

Liz Weston

Liz Weston

Even if you could somehow manage to stay off the radar, the Postal Service can find you. Thanks to the Postal Service's new "Every Door Direct Mail," businesses can send their ads to every home in a neighborhood. "Postage is as low as 14.5¢ per piece -- and you don't even need to know names or street addresses," the Postal Service crows on its website.

Use a prepaid envelope to opt out. "Any junk mail that has a prepaid return envelope, I put all their junk in that prepaid envelope and mail it back," one of my Facebook fans wrote. "Let them pay the postage, they usually get the idea."

Except they don't. The arm of the company that processes the returned envelopes is usually separate from the arm that handles the mailing list. Even if you pack the envelope with heavy stuff, hoping to cost the company more in postage, your protest typically will go nowhere other than the round file.

"You're sending it to the wrong spot," said Chuck Teller, the executive director of opt-out site Catalog Choice. "It feels good, but it doesn't work."

Ask to be taken off their mailing lists. Actually, this can work, although it's a hassle to call each company individually. The problem is the bad apples: the companies that ignore your requests, or worse.

Here's an illustration. Catalog Choice creates a unique email identity for each request it mails to companies on behalf of consumers. The mailbox that handles these requests has more than 650,000 responses, almost all of them spam, Teller said. In other words, companies are responding to the opt-out emails by sending more marketing messages.

"Email systems are messy, and most companies aren't being malicious," Teller said. "But we also can see Company A taking our opt-out email and selling (the email address) to Company B."

So what can you do that will make a real dent in the junk mail you receive? Here are seven options that work:

1. Opt out of (most) credit and insurance offers., operated by the major credit bureaus, allows you to remove yourself from the marketing lists the bureaus sell to lenders and insurance companies. You can delete yourself from these lists for five years at a time using the online form. To remove yourself permanently, you have to print out a form and mail it in. You have to supply your name and address.

The site suggests you also provide your Social Security number and birth date "to help to ensure that we can successfully process your request." Since the bureaus organize their databases using your Social Security number and birth date as identifiers, you probably want to provide those if you're serious about cutting down your junk mail. You'll still get offers, especially from companies that get your information from other sources. Still, you should see a noticeable decline in credit- and insurance-related junk mail, particularly if you've been inundated with it.

2. Take yourself off marketers', run by the trade association that represents direct marketers, promises to help remove you from the mailing lists maintained by the association's members. Basically, you'll be added to a "suppression list" that's provided to members to check against their mailing lists. Not every marketer participates in this program, but enough do that "it should reduce about 80% of the unwanted mail," said Senny Boone, the Direct Marketing Association's senior vice present for corporate and social responsibility.

Just ignore the website's advice about how you should "ideally" go about deleting yourself from marketing lists. It wants you to contact its hundreds of members individually. That way madness lies. Instead, use the button that allows you to unsubscribe from everything in each category: catalog offers, magazine offers and "other mail" offers. (The "credit offers" button takes you to

3. Consider signing up with Catalog Choice.
Once you buy a product from a retailer, chances are good you'll start getting its catalog, whether you're on a suppression list of not. Catalog Choice not only helps you get off those for free, but it also offers a $20-a-year MailStop Shield service that plucks your information out of several of the big databases, so it can't be sold to marketers. The company also has an iPhone application that makes getting off mailing lists relatively easy: You take a picture of the junk mail and send it in.

Catalog Choice has been a nonprofit since its inception a few years ago, although it's just been sold to TrustedID, an identity-theft protection company.

4. Pay attention to opt-out notices. Financial companies are required to send these once a year. The notices describe, in dry legalese, how the company collects and shares your information, and gives you a (usually cramped, sometimes tiny) form to fill out if you don't want your information shared. You're supposed to have to do this only once, despite the annual mailings.

5. Give anonymously. One big source of junk mail is solicitations for charitable contributions. Many nonprofits sell or trade donor information. You can opt out charity by charity, or you can give through a site such as Network for Good, which allows you to donate to any charity you choose without revealing your name, address or other details to that charity. Network for Good promises that it will use the information you provide only to make your donation and that it "will never sell, trade or rent your personal information to other individuals or companies."

6. Read privacy policies. What a snooze, right? Except you'll quickly find out which companies are sharing your information and which promise not to. Macy's privacy policy, for example, lists the many types of information it collects from customers (names, street addresses, email addresses, phone numbers, credit card numbers, birth dates, items purchased and information associated with the use of its website) and tells you the company "may share your information with third parties so that they can directly market their products or services to you if we feel that these products or services may be of interest to you."

Nordstrom, by contrast, "does not share customer information (including email addresses) outside the Nordstrom family of companies unless it is necessary to provide you with products or services available from Nordstrom. We may also disclose information when you tell us to do so, to identify or contact you, to protect your rights or the rights of Nordstrom or as required by law."

That doesn't mean you should stop shopping at Macy's. But if you don't want your information shared, you'll need to proactively opt out. You can do so by calling Macy's at 888-529-2254.

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7. Support legislation that would give you some rights. The Direct Marketing Association believes self-regulation is working just fine, but consumer and privacy-rights advocates disagree. Sens. John Kerry, D-Mass., and John McCain, R-Ariz., have introduced a Commercial Privacy Bill of Rights Act that says, among other things, that companies should have clear privacy policies and offer a way for consumers to opt out of information sharing. President Barack Obama's proposed Consumer Privacy Bill of Rights is another effort to give people some say in how their information is used. If you want some choice in the matter, let your lawmakers know.

Liz Weston is the Web's most-read personal-finance writer. She is the author of several books, most recently "The 10 Commandments of Money: Survive and Thrive in the New Economy" (find it on Bing). Weston's award-winning columns appear every Monday and Thursday, exclusively on MSN Money. Join the conversation and send in your financial questions on Liz Weston's Facebook fan page.