Nope. Welcome to the horror that is SMTP. It was adequate for its purpose in 1982 when Jon Postel specified it, but it's a little tired these days under the weight of the more varied uses it has since been tasked to.

Just as with a paper letter, the important delivery information is on the envelope. You can write two entirely different addresses on the envelope and the letter itself. The postal service will only ever look at the envelope address and attempt to deliver the letter to that address.

Unfortunately, in the world of SMTP, delivery to a post box is considered final. At this point, most mailers consider it acceptable to discard the envelope, and most post boxes do not support envelopes anyhow. You will regularly find that lists will contain a header "To:" field of the list address itself. And yet it is in your POP3/IMAP/local mailbox. What happened was that the mail transfer agent added two "envelope" lines a "To" and a "From" line. As the mail was passed from MTA to MTA, those lines were read and the mail routed. When it got to your mailbox, they were discarded, and only the body text was written. Although there are headers that say "To:" and "From:" - notice the colons - they are simply part of the body and were not parsed by the MTAs.

The solution to dealing with this is to modify the local delivery agent of your local MTA. A typical LDA used by the Sendmail MTA is Procmail. Note that modifying the LDA to preserve the envelope reciepient has potential privacy concerns due to exposure of BCC addresses.

Does that cover it?
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DrGoon