I run a gateway that delivers mail to a few different places, including two Exchange servers. Now, some users on one of the Exchange systems have managed to block certain senders, in a way that makes Exchange reject such messages with "554 5.1.0 Sender denied". The Exchange admins are trying to figure this out; in MOST cases blocking a sender results in messages being placed in a Junk folder, which is the behaviour we want. But sometimes, this happens. Anyway, getting Exchange to behave consistently is thankfully not my concern, nor the topic of this list.
So, if the Exchange admins cannot figure this out, we will become a backscatter source unless I can prevent Postfix from generating non-delivery notifications in these cases. To be precise, when a particular host (the Exchange server) is rejecting a message, I want Postfix to simply ignore that instead of sending a bounce. How can I do that? Or should I do something else instead? (Naturally, I don't want to suppress ALL non-delivery notifications, only those that arise in this particular way.) Ideally, I would want Postfix to reject those messages that Exchange is going to reject, but I don't see how that would be possible. (Exchange rejects after DATA.) Fredrik
