feedmail-deduce-bcc-where

feedmail-deduce-bcc-where is a variable defined in `feedmail.el'.
Its value is

nil

Documentation:
Where Bcc:/Resent-Bcc: addresses should appear in the envelope list.
Addresses for the message envelope are deduced by examining
appropriate address headers in the message. Generally, they will show
up in the list of deduced addresses in the order that the headers
happen to appear (duplicate addresses are eliminated in any case).
This variable can be set to the symbol 'first, in which case the
Bcc:/Resent-Bcc: addresses will appear at the beginning in the list;
or, it can be set to the symbol 'last, in which case they will appear
at the end of the list.

Why should you care? Well, maybe you don't, and certainly the same
things could be accomplished by affecting the order of message headers
in the outgoing message. Some people use Bcc: as a way of getting
their own "come back" copy of each message they send. If Bcc:
addresses are not handled first, there can be substantial delays in
seeing the message again. Some configurations of sendmail, for example,
seem to try to deliver to each addressee at least once, immediately
and serially, so slow SMTP conversations can add up to a delay. There
is an option for either 'first or 'last because you might have a
delivery agent that processes the addresses backwards.

You can customize this variable.