Hello,
Our company has a problem, where email sent from a specific external (non-O365) mailbox to our O365 mailbox results in NDR with error code #550 5.7.1 Unable to Relay. ATTR11 ##
Interesting thing is, that not all email gets rejected, but only random items.
Here's some diagnostic info from the external server, I could provide more if needed:
Generating server: external-address.com
external@address.com
AM3PR06MB210.eurprd06.prod.outlook.com #550 5.7.1 Unable to Relay. ATTR11 ##
Original message headers:
Resent-From: external@address.com
Received: from mail14-co1-R.bigfish.com (216.32.180.182) by
DB3PRD0611HT002.eurprd06.prod.outlook.com (10.255.185.35) with Microsoft SMTP
Server (TLS) id 14.16.353.4; Tue, 3 Sep 2013 08:17:30 +0000
Received: from mail14-co1 (localhost [127.0.0.1]) by mail14-co1-R.bigfish.com
(Postfix) with ESMTP id 611F38C009B for external@address.com; Tue, 3 Sep
2013 08:17:29 +0000 (UTC)<....>
Any idea how to solve this?
PS: Office 365 New wave, Plan E3.
Thanks,
Vinc