Question : Company cannot receive NDRs - filtered through Postini

Hello all -

Working on a weird issue I haven't seen before.

I currently have a client with a 2003 SBS Server running Exchange SP2. They smarthost through their ISP for outgoing mail, and incoming is filtered by Postini (it was their decision).

I re-configured their PIX firewall about 6 months ago when they cut over to Postini - I set it up to ONLY allow 25 traffic from Postini's mail servers. Has been working fine ever since. However - a few days ago the client contacted me and mentioned they no longer seem to be getting NDRs - sure enough - I hop in, start sending mail to bogus domains, invalid recipients at my domain, etc. - NO NDRs come back. Ever

I log into my gmail account - try the same test bogus e-mails, and I'm flooded with returned NDRs.

What the HECK could be causing this? I immediately told him verify with Postini and check to make sure all is well on their end. Their ISP/Smarthost pretty much said the same thing.

Anyone think of anything locally on the server, configuration wise I should be looking for? Or anyone can clarify anything? Aren't NDRs treated just like normal mail? Sending server of the NDR looks up MX Record, Goes to Positini, Postini sends it to client's public IP/mail server?

Any help would be much appreciated.

Answer : Company cannot receive NDRs - filtered through Postini

The problem is that you are sending email through the ISP.
The message goes to the ISPs server, which accepts it. Then when the message is rejected the ISP tries to send it back to the source - NOT the MX record. Most servers will now reject the email at the point of delivery, so the MX record is not involved.

The fix - either send email directly by DNS or use Postini as the outbound smart host so the NDRs can come back in again.

Simon.