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In most email clients you can send an e-mail to multiple recipients in the To: field by separating addresses by a semicolon.

You can also use CC to send a copy to other people. Is there any difference between the two? Do mail programs behave differently depending on whether you CC or multi-To?

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The answers imply it, but I'd like to spell it out explicitly: there is no technical difference between TO and CC, email addresses in both fields will receive the messages. –  Joachim Sauer Aug 22 '12 at 5:57
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@JoachimSauer: I think this is actually the answer the user was looking for ("Do mail programs behave differently depending on whether you CC or multi-To?"), and would be better as an actual answer. –  deworde Aug 22 '12 at 14:29
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BCC is the best ~_^ –  VISQL Aug 22 '12 at 15:51
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I would say CC is just an easy way of saying "FYI". The email might be of use to the person you CC'd but you're not talking to them. –  Mehrdad Aug 25 '12 at 8:43
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9 Answers

up vote 151 down vote accepted

It is described in RFC 2822, and more precisely section 3.6.3 of that RFC.

Here's the actual fragment that describes usage of "To" and "Cc":

The destination fields specify the recipients of the message. Each destination field may have one or more addresses, and each of the addresses indicate the intended recipients of the message. The only difference between the three fields is how each is used.

The "To:" field contains the address(es) of the primary recipient(s) of the message.

The "Cc:" field (where the "Cc" means "Carbon Copy" in the sense of making a copy on a typewriter using carbon paper) contains the addresses of others who are to receive the message, though the content of the message may not be directed at them.

The difference between "To" and "Cc" is in semantics, and determines how recipients should treat the message (as directed to them or "copied" only for their information).

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+1 for mentioning the RFC. –  kinokijuf Aug 22 '12 at 9:42
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RFC 5322 is the most recent –  makerofthings7 Aug 22 '12 at 15:04
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and +1 for mentioning semantics –  Joshua Drake Aug 22 '12 at 20:36
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It's worth adding that a lot of people's filtering/sorting rules look to see if their email is in the "To" or in the "CC" to help determine the priority of the message, and any other actions they may want performed. –  AnonJr Aug 23 '12 at 15:14
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Typically, if I am carbon copied on something, the email is not directing to me, but is information that I need to read. The email does not necessarily require my response, but rather the response of those who were in the TO field.

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The difference is mainly social and informative -- address the letter To some people, and send others a CC (carbon copy) so that they can be aware of the facts. Because it is a distinct header it is frequently used for filters, with CC mail being held to higher standards than To.

So, while it doesn't matter at the protocol level, it can determine whether a message gets sent directly to the trash, to a to be read if there's time folder or read immediately.

My rule of thumb is to put the person in the To header only if I directly address them in the body, otherwise use Cc.

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+1 for mention of CC: as a criterion for mail filtering. –  Justin ᚅᚔᚈᚄᚒᚔ Aug 22 '12 at 15:18
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Only if the recipient has told the mail program to handle them differently. They may choose to prioritize emails sent directly to them over ones they have been CCed on.

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The people you include in the To field should be the people you expect to read and respond to the message. The CC field should be used sparingly. You should only CC people who have a need to stay in the know. The BCC field should be used even more sparingly. People you include in the BCC field will not visible to others.

Cc stands for carbon copy and it means that whoever name appears after the Cc: will get a copy of the message. People who receive the mail can see who else is getting the copy of the message. The Cc header would also appear inside the header of the received message.

Bcc stands for blind carbon copy. With Bcc the recipients specified in this field do not appear in the received message. So all the recipients will get the message but cannot see others' name on the sent addresses.

From Answers Wiki.

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question is about cc/to - not cc/bcc –  Sathya Aug 22 '12 at 5:23
    
@Sathya fixed thanks for mention me my mistake :) –  avirk Aug 22 '12 at 5:37
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I hear what you are saying about BCC fielding being used more sparingly, but feel obligated to point out that in many cases, the world would be a better place if people used it more frequently. Specifically, when sending an email to a large group of people, sending it TO yourself and BCC'ing the large group prevents the inevitable reply all from one or more people followed by the reply all back asking people to stop ad nauseum. –  Foon Aug 22 '12 at 14:42
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When sending to a list it is preferred to use BCC rather than TO or CC as it prevents leakage of addresses to users you may not want to have your addresses. Thee message may be forwarded to lists that get capture by Spammers. –  BillThor Aug 23 '12 at 1:23
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@BillThor: there are a lot of people I'd like to force to read your comment. Very succinct description of the problem and its solution! –  iconoclast Aug 27 '12 at 16:32
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It depends on the e-mail client, and any post-processing rules the user has set up.

From the most general point of view, there is little difference in that the user receives the message either way (assuming everything is working the way it is supposed to, but if it's not working it would fail in either case the same way).

But if you want to pay attention to details, then they're not identical. The differences, or whether there are any differences, will vary from e-mail client to e-mail client. To give just one example, Lotus Notes will display a different icon in your Inbox depending on whether the message is addressed to you or you are receiving a carbon copy of it. This is a pretty trivial difference, which you may not care about. I mention it, however, because now matter how trivial, it is a difference in how one particular e-mail client handles the presentation of the mail.

More significant are differences based on e-mail rules that a user has set up. For instance, I've often created rules to divert messages from certain addresses to a folder I can ignore, unless I'm listed in the To: field. This is useful for junk mail that comes from within one's company. There are always those who think the whole company needs to know everything they're doing. But I want any e-mail from them that comes directly to me, especially if they're in management.

Differences based on mail rules will obviously vary from user to user, and again: you may not care about them. But if you want a thorough understanding of possible effects of putting an e-mail address in the To: or Cc: field, this is something you may want to consider.

You asked about the effects your choice of field will have on the e-mail client, but the biggest effect is the one it will have on the user. By putting a user's address in To:, you're communicating that the content of the message is directed to them, while by putting it in Cc: you're communicating that it's just an FYI. This affects what "you" means within the context of the message. If a message comes to me that says "you need to do such-and-such" then I take that to mean I have to do it. If it's addressed to someone else and I'm Cc:ed on the message, then I take that to mean the other person has to do it.

You didn't ask about the difference in meaning between To: and Cc:, but that difference in meaning is the underlying reason for any differences in the way an e-mail client handles the message, as subtle or negligible as those differences may be.

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+1 This is IMO the most objective answer to the OP's question 'Do mail programs behave differently depending on whether you CC or multi-To?' - '[...] Lotus Notes will display a different icon[...]' (Though I also do like the currently accepted answer due to the authoritative reference) –  Alberto Aug 24 '12 at 20:43
    
Thanks Alberto! I agree that the accepted answer is interesting and useful information, but excerpting the spec doesn't really answer a question about e-mail client behavior. The spec is prescriptive but the question is asking for something descriptive. That's what I tried to give in my answer. –  iconoclast Aug 27 '12 at 16:29
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Mainly we write the email ids in the "TO" field of those people whom we want to send the mail and we write email ids in "CC" field of those people whom we just want them to have an idea or knowledge of whatever has been written in that mail.

Lets say there is a software development team of 5 people including manager. Manager wants his team members to update the daily work status individually to him through e-mail.In this case, each employee will write an e-mail to the manager and he/she also want that e-mail to send to other team members so that they are also updated with the status. So he will write managers' email id in "TO" field and other team members' email ids in "CC" field.

So the intention was to send an email to the manager and not to everyone but just for the sake of the information we are sending it to each member. That's where we use "CC" field.

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There is a huge semantic difference between whether you are the recipient of a message or whether you are receiving a copy of it. For example, if an email says, "You must contact me by midnight or action will be taken", that applies to you if you're the person the letter was sent to. But if you were only sent a copy of a letter sent to someone else, then you are simply being notified by the sender that the recipient must contact them.

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If you set some mail ID as To field means you have some information to share with that particular person. CC (Carbon Copy) means that persons are related to your group.

Eg : In an org team leader send a mail to a particular person means he/she mention his/her id in TO field and other people who r working in the org as put in CC field. Other people also have the privilege to read that mail.

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