What Does BCC Mean in Email? How It Works and How to Use It

Short answer: BCC stands for blind carbon copy. Anyone you put in the Bcc field gets a copy of your email, but their address is hidden from everyone else, including other BCC recipients. BCC recipients can see the To and Cc addresses, a Reply All from anyone else won't reach them, and if a BCC recipient clicks Reply All themselves, everyone learns they were copied.

Below: how BCC works behind the scenes, what happens with replies, how to add BCC recipients in Gmail, Outlook, Apple Mail and on iPhone, and when BCC is (and isn't) enough to protect people's privacy.

What does BCC mean in email?

The name goes back to typewriters. A carbon copy was the duplicate made with a sheet of carbon paper, and a blind copy was one sent without the main recipient being told about it. Email kept both terms: CC for copies everyone can see, BCC for copies no one else can see.

The email standard, RFC 5322, defines the Bcc field as holding the addresses of recipients "whose addresses are not to be revealed to other recipients of the message." In practice that means:

Who	Can see To and Cc addresses	Can see Bcc addresses
To and Cc recipients	Yes	No
Bcc recipients	Yes	No, not even other Bcc recipients (at most their own)
The sender	Yes	Yes, in the Sent folder

Every recipient gets the same message body and the same attachments. BCC only changes who can see the addresses.

How BCC works behind the scenes

An email has two sets of addresses. The envelope is what mail servers use to deliver the message, a bit like the address on a parcel. The header is what you see in your email app: From, To, Cc, Subject and so on.

When you hit Send, your app hands every address (To, Cc and Bcc) to the outgoing server as envelope recipients, so all of them get a copy. The Bcc addresses are then left out of the header everyone else receives. The SMTP standard, RFC 5321, tells servers not to copy envelope recipients back into the header, precisely so blind copies stay blind.

RFC 5322 allows apps three ways to handle the Bcc line itself:

Remove it completely, so no copy shows any Bcc addresses. This is the most common.
Remove it from the copies for To and Cc recipients, but send BCC recipients a separate copy that includes a Bcc line. Some apps send each BCC recipient their own copy showing only their own address.
Leave an empty Bcc line, which tells recipients that someone was blind-copied without saying who.

This is why Google warns in its Gmail Help that recipients who don't use Gmail "may be able to tell" they were added to Bcc: their app may show the Bcc line in the copy they got. It's also why an email sent only to BCC recipients, with an empty To line, often shows "Undisclosed-recipients" in the To field. Apple's Mail guide describes exactly that.

What happens when someone replies

A To or Cc recipient clicks Reply All: the reply goes to the sender and everyone in To and Cc. BCC recipients don't get it, because their addresses were never in the header.
A BCC recipient clicks Reply: only the sender gets it. No one else finds out.
A BCC recipient clicks Reply All: the reply goes to the sender and everyone in To and Cc, from the BCC recipient's address. The secret is out.

That last case is the main risk the standard itself flags. RFC 5322's security section notes that a blind recipient has no explicit sign they were blind-copied, other than their address being missing, and "could potentially send a reply to all of the shown recipients" and reveal it. If you BCC someone, tell them not to reply to all. Forwarding works the same way: a forwarded copy shows To and Cc, not Bcc.

How to tell if you were BCC'd

Look at the To and Cc lines. If your address isn't in either, and the email wasn't sent to a mailing list you belong to, you were most likely blind-copied. Depending on the sender's app, your copy may also show a Bcc line with your address, or "Undisclosed-recipients" in the To field. If an email arrives this way, treat it as information for you, and reply only to the sender.

How to BCC someone in Gmail, Outlook and Apple Mail

Gmail

On a computer, click Compose.
Add your main recipients in To, then add hidden recipients in the Bcc field. The keyboard shortcut is Ctrl+Shift+B on Windows or Command+Shift+B on a Mac.
Write your message and click Send.

In the Gmail app on iPhone, iPad and Android, add recipients in the Cc and Bcc fields the same way (Google, Gmail shortcuts).

Outlook

New Outlook for Windows: open a new message or reply, then choose Options > Show fields > Show Bcc, and add names on the Bcc line.
Classic Outlook for Windows: in a new message window, select Options > Bcc. If the message opens in the Reading Pane, select Bcc on the ribbon. Once it's on, the Bcc box appears on every new message until you turn it off.
Outlook.com and Outlook on the web: select Bcc on the right side of the To line.
Outlook for Mac: select Bcc at the end of the To line. To show it on every message, go to Outlook > Settings > Composing and turn on Show BCC field by default.

Steps from Microsoft's help pages for Outlook for Windows, Outlook.com and Outlook for Mac. To check who you blind-copied later, open the message in Sent Items and look at the header.

Mail on Mac

Open a new message in Mail.
If there's no Bcc field, click the Header Fields button in the toolbar of the message window and choose Bcc Address Field.
Type the hidden recipients in the Bcc field. You can leave To empty; recipients then see "Undisclosed-recipients" in the To field.

These steps are from Apple's Mail User Guide for macOS 27 and are the same in macOS Tahoe 26 and Sequoia 15.

Mail on iPhone and iPad

In Mail, tap the compose button and add your main recipients in To.
Tap the Cc/Bcc, From field, tap Bcc, then enter the people you don't want other recipients to see.
You can also drag a name from To or Cc to the Bcc field if you change your mind.

To get a copy of everything you send, go to Settings > Apps > Mail and turn on Always Bcc Myself under Composing (Apple iPhone User Guide).

When to use BCC

Emailing people who don't know each other. Customers, parents, volunteers or event attendees shouldn't get each other's addresses. BCC keeps the list private and stops it being copied or harvested by anyone on it.
Avoiding Reply All storms. With the list in BCC, no one can reply to everyone by accident.
Letting someone drop off a thread. "Moving Sam to bcc" tells the group Sam saw the message and spares him the replies.
Keeping a copy for yourself or a shared archive, such as a CRM address or your own second account.
Quietly keeping someone informed, such as a manager. Do this with care: if it would look bad when discovered, and a stray Reply All could reveal it, forward the message afterwards instead.

When BCC isn't enough

BCC is easy to get wrong: one slip into To or Cc and every address is exposed. The UK data protection regulator, the ICO, notes in its email security guidance that forgetting to use BCC "frequently leads to the accidental disclosure of all the recipients' email addresses." It says BCC is useful but "not enough on its own to properly protect people's personal information", that it only hides addresses and does nothing for the content of the email, and that sensitive information should go through bulk email services, mail merge or secure data transfer services instead.

For newsletters or messages to hundreds of people, use a mailing tool or mail merge, which sends each person their own copy and can personalize it.
Mind sending limits: providers count BCC recipients. Gmail limits a single email to 500 recipients across To, Cc and Bcc (Google).
For sensitive content, use encryption or a secure sharing method. BCC hides who got the email, not what it says.

BCC vs CC

Both send a copy. CC recipients are visible to everyone and get Reply All replies; BCC recipients are hidden and don't. Use CC when the group should know who's reading, BCC when they shouldn't.

For what CC means, how to spell CCing, and CC etiquette, see our guide to what CC means in email.

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Frequently asked questions

Is BCC completely hidden?

From the other recipients, yes, as long as nobody slips up. The two leaks are a BCC recipient clicking Reply All, which shows everyone they were copied, and the sender putting addresses in To or Cc by mistake. Some apps also show a BCC recipient a Bcc line with their own address, so they can tell they were blind-copied.

Can BCC recipients see each other?

No. Each BCC recipient sees the To and Cc addresses but not the other BCC addresses.

Can I Reply All to an email I was BCC'd on?

You can, but your reply will go to the sender and everyone in To and Cc, and they'll all see you were copied. Usually you should reply only to the sender.

Why move someone to BCC?

To take them off the replies politely. They saw the message, the group knows they saw it, and Reply All won't keep landing in their inbox.

Do BCC emails get blocked?

Not because of BCC itself. But a message to many hidden recipients can hit your provider's sending limits, which count To, Cc and Bcc together (Gmail allows 500 recipients per email). For large lists, use a mailing tool.

How do I tell if I was BCC'd?

If your address isn't in the To or Cc line and the email didn't come through a mailing list, you were probably blind-copied. Some apps also show a Bcc line or Undisclosed-recipients in the To field.

Sources

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