Well, you could still use always_bcc and then pass that to an account
that uses procmail to dump anything not in the local domain, and copy
everything i nthe local domain to Maildir or similar.

If your mail server is very busy then this is probably not an elegant
solution, but you'd be able to figure this out. Postfix is generally
more efficient than sendmail anyway - so you;ve immediately got an
advantage.

Gooey