Hello List, I'll have to start by breaking to golden rule of this list and not posting postconf -n output as my question relates to a server over which I have no control.
A customer of mine is using a smart host provided by their ISP through which all outbound mail is delivered smtp.enta.net (which is running postfix). This server holds a list of valid domain from which this customer is allowed to send. A sensible precaution to prevent a compromised machine from sending spam using spoofed sender addresses on other domains. The problem is that when clients mail server sends a NDR the sender address is <> (ie NULL). The null sender address causes the message to be rejected with: 554+5.7.1+<>:+Sender+address+rejected:+Access+denied Is there a sensible way to configure postfix to allow these messages with null sender addresses to be relayed without opening the smart host up to exploitation? Or alternatively - and this is off topic for this list - is there a way to configure Microsoft exchange 2003 to send NDR's with a different sender address. And before anyone comments, yes I know this isn't best practice as NDR's should have null sender addresses to stop loops (bouncing bounce-backs!). Kind regards, James Day (IT Engineer)
