As an example of how sender_bcc_maps might be specified only in a single specific context, here is what I have been doing for some time now.
I wanted to generate BCC copies for every message submitted by my users (family members). In the "submission" stanza of my master.cf, I include the following option line: -o cleanup_service_name=msa-cleanup and then I include a corresponding new stanza in master.cf: msa-cleanup unix n - n - 0 cleanup -o sender_bcc_maps=hash:/etc/postfix/sender_bcc where my "sender_bcc" file contains entries such as the following: ri...@richw.org richw-...@richw.org and each recipient address (such as richw-bcc) is aliased to the regular address (richw) in /etc/aliases. The result is that BCC copies get created only upon local creation and submission of a new message, and not for anything received from the outside by smtpd. The name "msa-cleanup" (msa = mail submission agent) is arbitrary and could have been something else. And I didn't really need to use a separate set of "...-bcc" user aliases, though this turned out to be useful for Cyrus Sieve processing of the BCC copies. There may, I'm sure, be other variations possible here; I'm just showing this as one way to do it. Rich Wales ri...@richw.org