Email Filtering: A Brief Tutorial

My previous post generated a number of questions about how to maintain multiple email addresses. As I said there, using the same email address everywhere is not only an invitation to immense amounts of spam, it’s also a privacy problem, in that it allows cooperating site owners to link your accounts, just as Facebook and its Beacon partners are doing.

In addition to the privacy benefits, using unique email addresses helps counteract phishing attempts: You know that the “Fraud alert on your account” email is garbage if it’s not sent to the unique address you use only with your bank. Plus, if someone starts spamming you, or sells your address without your permission, you can just turn off the email address you gave them. (Note that I’m not talking about setting up multiple email accounts — creating say ten different Hotmail accounts which you then have to remember to check — but multiple addresses that point to a single account.)

I’ve been using unique addresses for more than a decade, managed with procmail, a very powerful Unix mail-filtering program that can do almost anything once you learn its arcane syntax. However, unless you’re a Unix geek in love with regular expressions like [A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,4} (which matches an email address) it probably won’t help you. But email has changed a lot in the last decade, and nowadays you can set up multiple email addresses without any technical knowledge at all, for free. Here’s an overview of how to do it.

If you have your own domain (meaning your email is something like, rather than or, the company that hosts it probably offers a way for you to create and manage multiple email addresses. This feature is usually called “aliasing.” It’s not the ability to create multiple mailboxes (almost every major Internet provider offers this, whether or not you have a domain) but the ability to create email addresses that can then be pointed to one or more mailboxes. The idea is that you can have more than one address, but have all the mail to those addresses delivered to a single mailbox. So you can set up “” and “” and so on, and have the email delivered into your regular mailbox, but set up filters so that mail with “” goes into an “Amazon” folder, and so on.

If you don’t have your own domain, you still have options. Consider Gmail, and remember the Secret Of the Plus Sign. Gmail’s spam filtering is unbelievably good; no matter how much spam you get at your Gmail account, you won’t be bothered by it, so you can use it without fear of spam. Gmail also has a pretty powerful filtering system that’s easy to use (not as good as procmail, but not bad, especially if you learn how to use Google’s search operators.)

And the Secret of the Plus Sign is this: and are the same address. Both will deliver to, but you can set up filters based on what follows the + sign. (This works on many email systems, not just Gmail; try it with your current email address. If your address is, send email to and see if it shows up. If so, you’re good to go.)

The bad news is that lots of sites, including Amazon and Facebook, will not accept + signs in email addresses. For those, I use a combination of aliasing and the plus sign. In other words, for amazon, create an alias “” and point it to “”.

Another option is available free from Yahoo. Yahoo mail has its drawbacks (inferior spam filtering and an ugly mail interface — if I liked Outlook I would use it) but it does have a feature that’s useful for this purpose. Under Options (top right of your Yahoo mail screen), choose “Mail Options,” select “Spam,” on the left side, and then click the “Set up a disposable address” link. This allows you to select a unique prefix and then allows you to create as many email addresses as you like using that prefix. Mail to those addresses can be delivered to your inbox or to a separate folder. My prefix is “kffile” so that means I could set up “” as my email address for Amazon, and have it filtered into an “Amazon” or a “Shopping” folder.

In short, it’s good practice not to use the same email address everywhere on the web, and with the wealth of options available, there is no reason to limit yourself to a single email address. For me, using multiple email addresses has not only meant that my inbox is essentially spam-free (fewer than a dozen spams a month), but also that Facebook’s privacy-invading system passed me by so completely I had to do some investigative work to find it.

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