Blind copying enables you to copy someone on a message without allowing the main recipient to see that someone else has received the message. It is the Bcc field (standing for blind carbon copy) on an email.
The Bcc field can be very useful for certain types of group mailings. When you send out messages to multiple people who do not know each other — for instance, a group of your company’s vendors — you can use the Bcc field to ensure that their email addresses are not revealed. If you don’t, in the worst-case scenario unscrupulous individuals may take those addresses and put them on their own mailing lists. Even if that doesn’t happen, though, it is simply good business to respect the privacy of the people you email.
Otherwise, be cautious in using the blind copying feature, as it is sometimes employed in ways that test the limits of business etiquette and ethics. Generally you should not blind copy someone if the recipient in the To field would be disturbed to discover that that person was surreptitiously included in the communication. If the blind copying does not serve an ethical and legitimate business purpose, avoid it. This issue becomes even more pressing if the recipient’s own messages are being passed on, without his or her knowledge, as part of an ongoing email dialogue that is being shared with invisible participants.
Finally, there is a technical issue to consider: if a blind-copied person clicks “Reply All” and sends a response, the original recipient may well receive that message, which would in turn reveal that the original sender blind copied someone on the email — a potential source of offense. A safer alternative is to send the original email, then go to your Sent box and forward the message to the third person.