[Macworld.com]

Forget who you’e Bcc-ed in a sent message? The header reveals all. [more]

[sdf]

Note that those receiving the message do not have the luxury of seeing this Bcc information so backstab and gossip all you like.
This is not always so. Many years ago when I tested sending email from an application I used to work on, I discovered that some email servers actually added the BCC header to the message. This was clearly a bug, and I think it's been fixed, but it's worth checking with your own email provider to make sure it's true. (I think it was a particular version of Groupwise, but it was a long time ago.)
(i.e. send an email without gossip BCCed to a few people and yourself, and seeing what the email you get looks like)

[forjohnc]

Does it really need all those steps to recover the BCc addressees? Using Mac MAIL (OSX Tiger) I just bring the SENT message up on the desktop and hit the REPLY ALL button. And there they all are.

[schoonerman]

There are three (or four) ways that the Bcc: header line can be handled by the sending mail program per the email RFCs (and not all programs follow the RFCs). All of these only have to do with the message as it "escapes" from the sending program ("Mail User Agent" or MUA), not what records the program may keep.
1. The header is stripped--the information is contained only in the message's "envelope" (the series of RCPT TO: commands in the SMTP dialog, which are not (properly) seen in the copy the recipient gets, except for his or her own copy in another header (often "Envelope-To:").
2. The Bcc: header is kept, but shows only the particular Bcc: recipient getting this copy of the message. That means the MUA has to emit a separate message for each Bcc: recipient.
3. The Bcc: header is kept, and included in the message as seen by the Bcc: recipients (who thus know about each other). I believe AOL mail did this at one time for mail which stayed internal to AOL--which is not controlled by the Internet RFCs that AOL ignored in their gateway for so long.
Possible 4. (It's lurking in the back of my mind, and I'm too lazy to check the RFCs.) A Bcc: header line is included but is empty for all recipients. (That is--others got this but I'm not telling you who.)
In no case should the To: or Cc: recipients see the Bcc recipiient information. (Which gets tricky in the receiving mail transfer agent, but is generally well implemented although at least some of those programs can be mis-configured by careless administrators.)
In any case, Mr Breen's method works for Apple's Mail.app. So does View-->Message-->Raw Source (toggled via Command-Option-U), which has the advantage that Mail isn't "helpfully interpreting" the addresses and other material--what you see is what is really there, in the order it is really in.
For Entourage 2004, a quick test suggests that you can't learn the Bcc's on mail you sent. At least, the equivalent of the method for Mail shows the message without the Bcc's. Perhaps there's a log lurking, or something.
I haven't looked at other programs.

[VidPro]

Quote:

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For Entourage 2004, a quick test suggests that you can't learn the Bcc's on mail you sent. At least, the equivalent of the method for Mail shows the message without the Bcc's. Perhaps there's a log lurking, or something.

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In Apple Mail, "send again" under Message in the sent folder (Shift-Command-D) will also reveal the BCC recipients, with the option of not actually sending the message if you only wanted to see the list it was sent to.
Would Entourage also have something like this?