Bounce emails are polite, but with spam these days, probably 98%+ bounce messages are to bogus addresses because they are spam with forged sender/reply to address.
By default, Zimbra bounces for unknown users which results in the spam message being sent along with the failed delivery message to be sent to whoever had the fortune of having their email address as the forged sender.
Not sure where I read it, but most mail admins will advocate that a better way to handle unknown user is to make postfix reject the email with a '550: Recipient Address Rejected: User unknown in local recipient table'. It is then up to the MTA that originated the connection to Zimra to determine what it should do with the email (spam).
This eliminates a lot of wasted traffic and makes Zimbra a good netizen for not bouncing spam around the internet.
So, my question, how can one configure Zimbra to give a 550 reject rather than a bounce?
In other postfix installations, I was able to do this using the local_recipient_maps setting like so (main.cf):
But this setting doesn't seem to work with default zimbra setup.
# Set this because this causes local postfix to generate a 550 reject
# response to the SMTP server that initiated the connection
# rather than sending a bounce email to a likely bogus address
unknown_local_recipient_reject_code = 550
local_recipient_maps = $virtual_mailbox_maps
Has anybody done this?