Hide addresses when sending mail (Bcc)
If you're sending a message to several people and want to hide each recipient's email address, you can use the blind carbon copy feature. When you're composing a message, just click Bcc in the top right corner of your compose window and enter the email addresses that you don't want recipients to see.
How you know when you've been Bcc'd
If somebody uses Gmail or Google Apps and they Bcc your address on an email, when you open the message, you'll see that you've been Bcc'd underneath the sender's name. Or, you can also check to see if you've been Bcc'd by clicking the "Show details" arrow underneath the sender's name, where you'll see your address in a Bcc: line.
Similarly, if an email sent by another Gmail or Google Apps user has reached you because you're a member of an email group that was Bcc'd, that group's address will show in the "Bcc" line.
Only your address (or the email group you have subscribed to) will be shown in the "Bcc" line; if any other email addresses were Bcc'd as well, you won't be able to see them.
Keep in mind that if you're Bcc'd on an email that was sent using another email program or service, Gmail may not be able to display this information.
How the people that you send email to will know that they've been Bcc'd
When you use Gmail to Bcc recipients on an email, we add a specific header for each individual Bcc recipient to let them know that they're receiving the email because they are Bcc'd on it. Each Bcc recipient only sees their own address in the message that they receive.If the recipients use Gmail or Google Apps to read their mail, they'll see this header. Otherwise, depending on how their email systems handle the header, recipients may or may not see the information.