Author Topic: What Happens with Bcc?  (Read 1009 times)

What Happens with Bcc?
« on: February 09, 2020, 05:18:26 pm »
If I send an email to various recipients, some in the straightforward 'To:' category, and some in the 'Bcc:' category, and then a recipient in the former group replies to all, does their reply go to the recipients in the 'Bcc:' group in the original email?  Does it make any difference if some one in the 'Bcc:' group replies to all?

Re: What Happens with Bcc?
« Reply #1 on: February 09, 2020, 05:26:50 pm »
Nope. The bcc are hidden from everyone else.
If you don’t make time for exercise now, sooner or later you’ll need to make time for ill health.

Re: What Happens with Bcc?
« Reply #2 on: February 09, 2020, 06:33:21 pm »
Reply all won't go to any other BCC recipients of the original message.  It will go to CCed recipients.

pdm

  • Sheffield hills? Nah... Just potholes.
Re: What Happens with Bcc?
« Reply #3 on: February 09, 2020, 06:38:32 pm »
With cc: <address list> the addresses of all the recipients in the <address list> and the sender are available and visible to all cc: recipients. They can thus "reply to all" if they want.
With bcc: <address list> only the sender address is visible anywhere in the message headers. The only reply the recipient , as a member of the bcc: <address list>,  can make is to the sender.

Kim

  • Timelord
Re: What Happens with Bcc?
« Reply #4 on: February 09, 2020, 06:41:15 pm »
With bcc: <address list> only the sender address is visible anywhere in the message headers. The only reply the recipient , as a member of the bcc: <address list>,  can make is to the sender.

I don't think that's true.  BCC addresses don't appear in the headers, but any additional To or CC addresses will.
Careful, Kim. Your sarcasm's showing...

Re: What Happens with Bcc?
« Reply #5 on: February 09, 2020, 07:32:09 pm »
RFC2822* says only Bcc is removed when the messages are sent. A server stripping out the To and CC fields wouldn’t be compliant.

(* anyone else hear an owl?)

pdm

  • Sheffield hills? Nah... Just potholes.
Re: What Happens with Bcc?
« Reply #6 on: February 09, 2020, 08:16:17 pm »
Yes, you are right. cc: and bcc: act independently and exclusively of each other. Sorry I did not make that clear!

Re: What Happens with Bcc?
« Reply #7 on: February 09, 2020, 09:29:52 pm »
So, I'm wondering then if, though the replier may not know, and will not see, the recipients under Bcc, will they actually receive the reply?

Re: What Happens with Bcc?
« Reply #8 on: February 09, 2020, 10:05:37 pm »
So, I'm wondering then if, though the replier may not know, and will not see, the recipients under Bcc, will they actually receive the reply?

No, they can't. The recipients have no way of knowing who was in Bcc, and no reply can include email addresses that aren't known.

Obviously if a message isn't addressed to you, yet you receive it, it's highly likely you were Bcc'd in. You still have no way of knowing who else was Bcc'd in.
Quote from: Kim
Paging Diver300.  Diver300 to the GSM Trimphone, please...

Re: What Happens with Bcc?
« Reply #9 on: February 09, 2020, 10:31:17 pm »
So, I'm wondering then if, though the replier may not know, and will not see, the recipients under Bcc, will they actually receive the reply?

A reply is a new message and your mail app has to construct the list of people to send it to. If it doesn't know the BCC'ers addresses, it can't send it to them.

It's only really associated with the previous message at the far end, assuming the recipient has both messages available. There's no concept of a reply in the delivery system.

quixoticgeek

  • Mostly Harmless
Re: What Happens with Bcc?
« Reply #10 on: February 10, 2020, 11:38:51 am »

A reply is a new message and your mail app has to construct the list of people to send it to. If it doesn't know the BCC'ers addresses, it can't send it to them.

It's only really associated with the previous message at the far end, assuming the recipient has both messages available. There's no concept of a reply in the delivery system.

Specifically, the only way that any system knows about the concept of a reply is from the "In-Reply-To:" header. But this is only used by the client at either end, the servers in the middle don't do anything with it.

J
--
Beer, bikes, and backpacking
http://b.42q.eu/

Kim

  • Timelord
Re: What Happens with Bcc?
« Reply #11 on: February 10, 2020, 12:12:04 pm »
Specifically, the only way that any system knows about the concept of a reply is from the "In-Reply-To:" header. But this is only used by the client at either end, the servers in the middle don't do anything with it.

And all too frequently, neither do the users.  (You know the ones who reply to any old message from the person/list at random, completely breaking the threading.)
Careful, Kim. Your sarcasm's showing...

quixoticgeek

  • Mostly Harmless
Re: What Happens with Bcc?
« Reply #12 on: February 10, 2020, 12:26:57 pm »
+ for Koolstop Salmon.  Not sure that they perform much better than the stock ones, but they seem to eat the rim a lot less.

Completely agree with you Kim.

At least it's not easy to do on forums like this...

J
--
Beer, bikes, and backpacking
http://b.42q.eu/

Re: What Happens with Bcc?
« Reply #13 on: February 10, 2020, 06:11:02 pm »
+ for Koolstop Salmon.  Not sure that they perform much better than the stock ones, but they seem to eat the rim a lot less.

Completely agree with you Kim.

At least it's not easy to do on forums like this...

J

Now that should confuse everyone  ;)

Re: What Happens with Bcc?
« Reply #14 on: February 10, 2020, 06:38:20 pm »
+ for Koolstop Salmon.  Not sure that they perform much better than the stock ones, but they seem to eat the rim a lot less.

Completely agree with you Kim.

At least it's not easy to do on forums like this...

J

Do koolstop salmon stop the reply all emails?
If you don’t make time for exercise now, sooner or later you’ll need to make time for ill health.

Re: What Happens with Bcc?
« Reply #15 on: February 10, 2020, 06:55:48 pm »
But if I read Martin's original question correctly; if person A sends an email to people B & C with a copy (cc) to person D and a blind copy (bcc) to persons E & F. What happens when each of these people hit a reply to All?

people B, C and D will reply to A, B, C, & D excluding themselves as they do not know that E or F was bcc'd. However to whom would a reply to all from person E go? The email they received will contain the full list of sender A, recipients B & C and the copied in D but not F so does their reply go to all these people or just the original author?

My instinct is that the reply would go to A, B, C and D and thus break the anonymity they had as a bcc recipient.

Re: What Happens with Bcc?
« Reply #16 on: February 10, 2020, 06:58:32 pm »
The simple answer is not to reply unless you are on the to line and specifically have been asked something. Otherwise it’s just for info and can probably be sent straight to the bin after a quick glance.
If you don’t make time for exercise now, sooner or later you’ll need to make time for ill health.

Kim

  • Timelord
Re: What Happens with Bcc?
« Reply #17 on: February 10, 2020, 07:24:30 pm »
people B, C and D will reply to A, B, C, & D excluding themselves as they do not know that E or F was bcc'd. However to whom would a reply to all from person E go? The email they received will contain the full list of sender A, recipients B & C and the copied in D but not F so does their reply go to all these people or just the original author?

My instinct is that the reply would go to A, B, C and D and thus break the anonymity they had as a bcc recipient.

That's correct.
Careful, Kim. Your sarcasm's showing...

Re: What Happens with Bcc?
« Reply #18 on: February 10, 2020, 07:32:26 pm »
But if I read Martin's original question correctly; if person A sends an email to people B & C with a copy (cc) to person D and a blind copy (bcc) to persons E & F. What happens when each of these people hit a reply to All?

My understanding is that people E&F are invisible to B,C & D as long as they don't hit the "reply to all" button, in which case, all others will understand that they were Bcc'd.

A

Re: What Happens with Bcc?
« Reply #19 on: February 10, 2020, 08:32:48 pm »
if person A sends an email to people B & C with a copy (cc) to person D and a blind copy (bcc) to persons E & F. What happens when each of these people hit a reply to All?
The Bcc information is not present in the email received by any of B, C, D, E or F.  Any reply from B, C or D will not go to E or F. If E, say, were to reply that would reveal E to any of B, C or D that got the reply, however E cannot reply to F and a reply from E will not reveal F.

The Bcc information could be retained by A's email program, but if that happens I would expect A's email program to continue to treat E and F as blind in any reply sent by A.

Caveat emptor: the email standard isn't standard and email implementations, both client and server, have interesting variations.

Re: What Happens with Bcc?
« Reply #20 on: February 10, 2020, 09:33:26 pm »
But if I read Martin's original question correctly; if person A sends an email to people B & C with a copy (cc) to person D and a blind copy (bcc) to persons E & F. What happens when each of these people hit a reply to All?

My understanding is that people E&F are invisible to B,C & D as long as they don't hit the "reply to all" button, in which case, all others will understand that they were Bcc'd.

A

simply, no.

Re: What Happens with Bcc?
« Reply #21 on: February 11, 2020, 06:22:07 am »
simply, no.

Could you explain please? Maybe I was not clear enough. It is E & F who should not reply to all if they wish to remain anonymous. B,C &D can reply to all if they wish, E&F will not receive anything and B, C&D will never know that E or F exists. Right?

Re: What Happens with Bcc?
« Reply #22 on: February 11, 2020, 07:41:47 am »
simply, no.

Could you explain please? Maybe I was not clear enough. It is E & F who should not reply to all if they wish to remain anonymous. B,C &D can reply to all if they wish, E&F will not receive anything and B, C&D will never know that E or F exists. Right?

OK. For starters, E will never, ever see F in your scenario, so will not know that F was on the address list. Next, you have to do more than reply all, as a bcc most implementations will not "Reply all" to any but the sender, you will have to add the B, C & D names manually (even if they are in the "To" field as opposed to cc). Not guaranteed, clearly, as it is in the software implementation but most mail clients will work as they are supposed to.

Jaded

  • The Codfather
  • Formerly known as Jaded
Re: What Happens with Bcc?
« Reply #23 on: February 11, 2020, 08:22:44 am »
(click to show/hide)
If you don't like your democracy, vote against it.

Re: What Happens with Bcc?
« Reply #24 on: February 11, 2020, 08:27:23 am »

A reply is a new message and your mail app has to construct the list of people to send it to. If it doesn't know the BCC'ers addresses, it can't send it to them.

It's only really associated with the previous message at the far end, assuming the recipient has both messages available. There's no concept of a reply in the delivery system.

Specifically, the only way that any system knows about the concept of a reply is from the "In-Reply-To:" header. But this is only used by the client at either end, the servers in the middle don't do anything with it.

The servers in the middle don't do anything with the To: or CC: fields either, they too are purely decorative.

The email addresses that emails are intended to be delivered to are controlled by the "RCPT TO <address>" SMTP commands sent by the client. Most email clients derive these values from the To: cc: and Bcc: fields in the message composition interface but that's not a strict requirement, which is why it's so easy to fake emails. The "From:" field is decorative too, the SMTP command is "MAIL FROM <address>" although the value supplied to the "MAIL FROM" command is usually stored in an extra header (MFrom: ?)

bcc: is implemented by telling the servers you want to deliver email to an address ("RCPT TO") but just not mentioning it anywhere in the headers.

A postal analogy would be roughly something like this:-

From: A
To: B
CC: C,D
BCC: E,F

A writes out 5 postcards all the same.
All 5 are addressed "From: A, To: B,C,D".
Then put each postcard in an envelope, each envelope is addressed to one of B,C,D,E,F with return address "A" on the back.
A sticks them all in the post.

For any of the individual recipients the outer envelope just has their name on it. Once they open the envelope they find the postcard that says it was sent from A to the group B,C,D.

The rough analogy is that the email you compose in your client may look like it is one item being sent to multiple people but it is actually wrapped up in a separate communications layer that is point to point.

You may think you're sending one email but if you send an email to 3 people (one hotmail.com, one gmail.com, one example.com) then you may contact your outgoing mailserver once but from that point on it will be dealt with as 3 separate emails.

But if I read Martin's original question correctly; if person A sends an email to people B & C with a copy (cc) to person D and a blind copy (bcc) to persons E & F. What happens when each of these people hit a reply to All?

My understanding is that people E&F are invisible to B,C & D as long as they don't hit the "reply to all" button, in which case, all others will understand that they were Bcc'd.

A

simply, no.

Umm, sort of "yes".

If A sends an email to B,C&D (either To: or CC:) and then E&F by bcc: then if E does "reply to all" then it will go To: "A" and CC: "B,C&D". So B,C&D will now know that E was probably bcc'd on the original email (or had it forwarded to them by someone, the quoting that the various clients use may make this more obvious - or not).

But B,C&D (or E) won't know F was also bcc'd on the original email unless F also replies to all (or somehow lets on they received the original).
"Yes please" said Squirrel "biscuits are our favourite things."