If you read this, you have probably spread my email address too liberally. Below, I explain how this helps spam to grow in volume, and how you can avoid that in the future.
The privacy laws in most countries protect personally identifying data, including email addresses. It is "not done" to spreak such information freely. Of course there are gray areas, but if I sent you a reference to this page then you've clearly been wrong. A common mistake, which does not make it any less bad, is sending email to many people who hardly know each other, in such a way that each sees the others' mail addresses.
Before privacy laws protected this, there has always been so-called netiquette, which (among others) comes down to mindfulness when handling someone else's privacy. These rules were founded on good reason, and in fact prescribed generally acceptable behaviour.
By ignoring these matters, you give evidence of a certain degree of neglect to these principles. So don't be surprised if at some point you receive a sharp response from someone who understands how email and spam operate on the Internet. They understand the problems caused by behaviour such as yours.
There are worse situations; some people make the additional mistake of writing to many people "so at least enough will see it", for example by posting to an email list that includes the intended recipients, as well as others. This results in (many) readers having to decide that the email is not intended for them, and the only reason for that work is that the sender was too lazy to address the right people directly. This is in fact a waste of someone else's time. Luckily this is not very common.
We all know spam as the annoying problem of unsolicited offers sent to our mailbox. Those who use a spam filter know that this is only a partial solution; sometimes a good email gets blocked and discarded.
Spam works by sending a message to masses of people, and this is possible because email is a free medium. Since the expenses are zero, there are no boundaries to the number of people that can be addressed, so a spammer will aim to post to every mail address on the planet.
The commercial model of spam works so well that it has ignited a secondary market, on which email addresses are sold. This market is serviced by parties who write computer virusses just to collect email addresses. Such virusses are not even very hard to write; most people use the default setup from their computer sales channel, already happy to have gotten that to work. These same people are not always good at updating their virus-scanning software either. Furthermore virus scanners always chase after the fact, because a virus must be out in the open before it can be caught. The raprid spread of a new virus on the internet makes it possible for them to do a lot of damage, or collect a lot of information, before they are stopped.
When you link relatively unknown people by sending them each other's email addresses, you expose them to quite a lot of extra chances of being shown to such virusses, which is precisely why it is important to practice some caution before sending one person's email address to someone else. We shouldn't let the world come to a grinding halt, but submitting lists of email addresses to people who don't know each other is plain carelessness. It is paving the way for spammers.
Interestingly, there are quite a few solutions to avoid this problem, but neverthless the is a continuous flow of people who screw up. After having seen how it works people tend to understand, but in fact this is too late if this is in reaction to a mail mistake. Towards the future it is better to learn the right behaviour, and perhaps spreading this knowledge could help to make up for a mistake that cannot be reverted.
Ccaddresses, but to use
Bccinstead -- blind carbon copy, meaning recipients that are not mentioned in the email. Behind
Toyou could put your own email address. This is the simplest solution, which works without a need to setup anything.
Bcc. You can also use this if you forgot to send mail to someone in your original email.