Is anyone seeing this error lately? It seems to have started for us after installing rollup 3, but I can't confirm the exact timing. We are also now seeing a 421 4.4.0 remote server response was not rfc conformant. I've done all the RDNS checking, blacklist checking and we are not blocked anywhere. It's not a cert issue, not tcp offload. Clues?

And the answer is.... Our Cisco ASA5510 was replaced with a new one after a failure. For some odd reason Inspect ESMPT got turned on. This causes the Cisco to replace non rfc conformant responses to be replaced with 220-********************** which our Exch2k7 server interprets as a bad response, connection dropped. Solution is to turn off Inspect ESMTP Cheers