You can blind carbon copy (BCC) people on an email without the main addressees knowing about it. The story of the blind carbon copy function is another example of real world processes imaging themselves in the virtual world.
The simple term "carbon copy" comes from the days of manual typewriters, when copies were made by typing on paper with several layers. Between each layer of paper was a thin sheet with carbon on the bottom side, so that when the typewriter keys hit the paper, the impact made a "carbon copy" of the letter on the paper sheet underneath. When you were finished typing a page, you would separate out the paper and throw away the carbon sheets, almost always getting some of the black carbon all over your hands.
You could get two, three, and four layer carbon copy paper, and even some very thin six layer paper. The top paper got the typewriter ink and looked the best. The top carbon copies always looked much crisper than the lower copies, as the force of the typewriter key strike dissipated through the layers. Occasionally, by accident or design, an extra carbon copy would be given to someone not on the official CC carbon copy address list. Because there was no way the official addressees could know about these extra copies, they were called "blind carbon-copies" (BCC).
It turned out that people liked this feature so much they built it into email. If you put addresses in the BCC field of an email it will be secretly copied to those addresses, and none of the other addresses in the To, CC, or BCC fields will know about it because the BCC field is not displayed on incoming messages.
Some of the ways that the BCC field can be used are listed below:
If you don't enter at least one valid email address in the To or CC field, then some email programs will indicate a notation like "Recipient list suppressed" in the To field, which tells the recipient at least that there are BCC addresses. If you don't want that to happen, you need to enter at least one valid email address in the To field, such as your own address, perhaps with a custom text description like the following:
To: "Gardening Friends" <firstname.lastname@example.org>
Note there is a potential security flaw in the BCC feature. According to the conventions of the SMTP protocol, all addresses, including BCC addresses, are included in every email as it is sent over the Internet. The BCC addresses are stripped off blind copy email only at the destination email server. Therefore, if the addressee controls their email server or can access it, they could examine the BCC addresses on every email they receive. SMTP is designed this way for a couple of reasons:
Very occasionally, an email server will be misconfigured and not strip off the BCC list on email it sends to its local users, revealing the complete blind copy address field to users that receive the email at that domain. Therefore, BCC is very good but not perfect at keeping addresses confidential, and should not be relied on for the most critical and sensitive of communications. To avoid this problem you can always send the email to the main addressee, and then forward it old fashioned-way to those that you wish to have a copy.