Hi
My organisation doesn't use Office 365, but some people we deal with do. We're seeing thier email being bounced intermittently by both of our mail gateways and by our ISP's store-and-forward backup relay.
When the message fails, it's last hop before reaching us is from a server that appears to not have a DNS entry- one example is DB3PR01MB137.eurprd01.prod.exchangelabs.com. If I try to ping that by name it doesn't resolve, and when I did a routine DNSRBL lookup on it at https://toolbox.surftown.com/cgi-bin/rbl.cgi that fails to resolve it too- but I find this very strange.
I'm pretty certain having an unresolvable address as the sending address will cause all sorts of issues- using the RBL checker against my MX resolves both the forward and reverse DNS correctly.
Note that the failure only happens intermittently. Mail that succeeds seems to come from another range-
emea01-am1-obe.outbound.protection.outlook.com
but when it fails, the generating server is something like DB3PR01MB137.eurprd01.prod.exchangelabs.com, which has been denied relaying by our our ISP's server, having presumably been rejected by our gateway because DNS doesn't resolve. Any ideas?
I've previously posted this at http://answers.microsoft.com/en-us/outlook_com/forum/oemail-osend/office-365-outgoing-server-dns-entries/e6141595-cb58-41eb-8bb6-cf98a66b4e36?msgId=81a29763-4e17-4d3a-b158-1be7dea2fa27 but it was suggested I post here- this forum seemed the best match.
Thanks
Chris