In this instance, you would probably want to use a truly anonymous remailer, where even the operator of the server does not know your identity. They also have the drawback that recipients cannot respond to you. If you are posting to newsgroups that won't be a problem, but if you wish to receive a reply you will need to establish what is called a nym account, a free e-mail account on the server nym.alias.net. For most Internet users, pseudo-anonymous remailers are more than adequate. Not everyone uses remailers for legitimate purposes.
Some people use anonymity to send hate mail, porno graphic images, or spam.
Complaining to remailer operators and asking them to identify the sender will not provide much satisfaction. Often, however, you can request that operators block any mail from their service from being sent to you in the future. Like many services on the Internet, anonymous remailers can serve very useful functions or they can be abused. MIT expects members of its community to use remailers and other Internet services responsibly.