If you’re using the always_bcc parameter in postfix for whatever quick-n-dirty scheme you’ve come up with you may want to add multiple destinations there.
You’ll get errors if you try any of the normal postfix syntaxes for specifying multiple addresses, with spaces, commas, whatever.
The trick is to put an alias in here and then put your expansion in /etc/aliases.
For instance, in main.cf:
always_bcc = alwaysbcc
and then in /etc/aliases:
alwaysbcc: bob@example.com, alice@example.org