G'day all I'm seeing the most bizarre behaviour that I've ever seen with LISTSERV. When a post hits one of our lists it appears to get resent to *most* of the recipients without any problems except for a few. For these few, it appears that the mail server gets a very confused DNS response and thinks the mail exchanger for their domain is actually our LISTSERV box. It then happens to the next recipient, and the next, and the next, ad nauseum. The resulting header starts to look like this: Your message To: [log in to unmask] did not reach recipient This mail domain has following registered mail servers: Mail eXchange host:listserv.towersoft.com.au priority:0 After command RCPT TO: <[log in to unmask]> Server responded:>550 Recipient not local. and quickly grows to look like this: Your message To: [log in to unmask] did not reach recipient This mail domain has following registered mail servers: Mail eXchange host:listserv.towersoft.com.au priority:0 After command RCPT TO: <[log in to unmask]> Server responded:>550 Recipient not local. After command RCPT TO: <[log in to unmask]> Server responded:>550 Recipient not local. After command RCPT TO: <[log in to unmask]> Server responded:>550 Recipient not local. After command RCPT TO: <[log in to unmask]> Server responded:>550 Recipient not local. After command RCPT TO: <[log in to unmask]> Server responded:>550 Recipient not local. After command RCPT TO: <[log in to unmask]> Server responded:>550 Recipient not local. After command RCPT TO: <[log in to unmask]> Server responded:>550 Recipient not local. After command RCPT TO: <[log in to unmask]> Server responded:>550 Recipient not local. After command RCPT TO: <[log in to unmask]> Server responded:>550 Recipient not local. After command RCPT TO: <[log in to unmask]> Server responded:>550 Recipient not local. After command RCPT TO: <[log in to unmask]> Server responded:>550 Recipient not local. After command RCPT TO: <[log in to unmask]> Server responded:>550 Recipient not local. After command RCPT TO: <[log in to unmask]> Server responded:>550 Recipient not local. After command RCPT TO: <[log in to unmask]> Server responded:>550 Recipient not local. After command RCPT TO: <[log in to unmask]> Server responded:>550 Recipient not local. After command RCPT TO: <[log in to unmask]> Server responded:>550 Recipient not local. After command RCPT TO: <[log in to unmask]> Server responded:>550 Recipient not local. After command RCPT TO: <[log in to unmask]> Server responded:>550 Recipient not local. After command RCPT TO: <[log in to unmask]> Server responded:>550 Recipient not local. After command RCPT TO: <[log in to unmask]> Server responded:>550 Recipient not local. After command RCPT TO: <[log in to unmask]> Server responded:>550 Recipient not local. After command RCPT TO: <[log in to unmask]> Server responded:>550 Recipient not local. After command RCPT TO: <[log in to unmask]> Server responded:>550 Recipient not local. After command RCPT TO: <[log in to unmask]> Server responded:>550 Recipient not local. A quick scan of the logs confirms that the individual mails are attempting to be sent right back to LISTSERV where it naturally generates an error to me. There seems to be some correlation between the alphabetical order of the recipient domains. (Is this how LISTSERV decides where to split bundles of subscribers into smaller files?) Apart from that there's no discernable similarities between occurances. If it applied to the same list or subsriber(s) I'd have someplace to look for an answer but I've no idea where to go next. I've checked our internal DNS - the MX records are correct. I've checked our external DNS - same thing. I've checked with our ISP's DNS - everything's in order. I did an NSLOOKUP to try and find a prority=0 mail exchanger (as seen in the header) with no result. Is anyone able to help? Is it LISTSERV that's the culprit or am I barking up the wrong tree? Any suggestions are welcome. Feel free to reply off-list if you wish. Chazzozz!! Michael Shannon Webmaster [log in to unmask] "Nature has provided us with two ears, two eyes, and one tongue, to the end that we should hear and see more than we should talk." - Socrates Note: Opinions expressed on this list are my own and do not reflect the views, opinions or position of my employer. If swallowed, seek medical advice.