Significance of "Envelope-to"

[John Drabik]

Hello all,
    Although this is not specific to PMMail, I wonder if there is
anybody on the list who can answer the following e-mail question:

   I received a message (unexpectedly), where I was *not* listed in
either the "To:" list, or the "CC:" list, when looking at the message
in PMMail, and with a raw text editor.  However, my e-mail account
*is* listed in the "Envelope-to:" section.  My question is this: Is
it possible that someone could have unwittingly sent me this (rather
sensitive) e-mail without being aware of it, and if so, what would be
the mechanism to create or send such a message?  How does one
manipulate the "Envelope-to:" section, and can it effectively act as
a "blind-copy"?

   Any response would be greatly appreciated - this is a matter of
rather pressing importance, and I would like to know how this type of
"error" could have occurred, how to determine if it can happen again,
and what to do about it.

   THANK YOU FOR ANY HELP YOU CAN PROVIDE!!!

John Drabik