The Internet Is Not Private
Generally speaking, every email you send travels from server to server, across the internet, as clear text. That is to say the email is an ASCII document--just a text file. With the simplest tool--notepad.exe--anyone along the way can read your message. Not only is your mail readable by all, it's pretty much impossible for you to send your message without also including information pointing directly to yourself as the message origin. A bogus email address isn't enough. You IP address, by necessity, accompanies your message the entire route. If you value your privacy, you take extra measures. That's where anonymous remailers come in. A remailer message cannot be traced to you. Your privacy is intact.
Enter, The Remailing Service
I know--you've been told that it's impossible to make a message untraceable. Well, technically speaking, yes, for all but a very few extremely talented individuals, it is impossible. However, listen to this. What if there was a service where you could send your message, that would take it, remove all traces that it's from you, replacing that info with it's own. The service then forwards the message to the recipient stating it's from an anonymous sender. Now, that message isn't from you. It's from the service. No technical wizardry required.
That's exactly what a remailer does! Of course, you may have concerns that if there's some uproar caused by your message, the remailer operator will give you up to avoid problems. In the scenario above, that might be possible. Of course, the remailer network is composed of operators who say they won't give you up. In fact, so that they can't be force to provide compromising info, they don't keep any mail logs. Should they be presented with papers requiring they give info regarding a message, they cannot give what they don't have. Most remailers handle thousands of messages a day. Without logs, there is simply no way the info can be had.
How About A Chain Of Several Remailers
One remailer is good, but we want more security. Who knows, maybe the remailer operator is actually some MIB, or other legal entity, trying to catch unwary users. That could happen. There's no requirement in the network that operators prove they are legitimate. Instead, the system is designed with the expectation that some remailers are owned by unfriendly forces. That's why we don't settle for a single remailer. We use a chain of three or more remailers through which we send our message. This is the secret to the truly anonymous message.
Here's how it works: Mixmaster picks a series of remailers for your message. Then it encrypts your message, along with recipient info using the cryptographic key of the last remailer in the chain. That remailer will deliver the message to the recipient. Then mixmaster takes that encrypted message and encrypts it again, but this time to the next to last remailer in the chain. When that remailer decrypts the message, it finds an encrypted packet with instructions to that last remailer in the chain. This process continues, stepping back from the last remailer in the chain, one by one, until the first remailer is reached. That's the remailer you will actually send the multi-encrypted message to. This results in the multi-encrypted packet I've mentioned earlier. Each remailer knows only that it got an encrypted message from remailer A and sent it to remailer B. That is to say, they'd know that if they were to keep logs. None of the remailers, short of the last, has any idea what is in your message or who the recipient is. The last remailer handles the message in clear text. This is necessary so that the recipient can receive the message unencrypted. This clear text stage can be eliminated by PGP encrypting the message prior to starting the send. In that case, the recipient must have a key or password to decrypt the delivered message. This situation can arise when known parties are communicating via remailers.
There's a great deal of security involved in this process. In order to actually determine the sender of the message, it would be necessary for the message to be traced back through the series of remailers used. That's not going to happen. One could even take this a step further and select a chain of remailers each of which lives in a different country. This could make it more difficult to get cooperation of local law enforcement from remailer to remailer.
But...How Many Remailers?
The number of remailers in your chain should be determined by your security needs. If you're simply posting reasonable articles to the USENET, you may only need two. If you're a spy, and secrecy is imperative, you may need four or more. When deciding chain length, a rule of thumb is: the greater the number of remailers, the more likely the message will be lost and not delivered. The fewer the number of remailers, the less secure the privacy. You need to evaluate your needs yourself. Three remailers is a good general purpose chain.