This is going to be a very brief post. I’m currently setting up Nagios to do some network monitoring at my place of work. Several weeks ago, I had upgraded our Exchange 2003 mail server to Exchange 2010. Our e-mail distribution groups were all mail-enabled security groups with global scope. I hadn’t bothered to upgrade them yet to mail-enabled security group with universal scope. I initially had Nagios sending notifications to a particular pre-existing mail-enabled security group that was created when Exchange 2003 was in production. Notifications flowed to members of the distribution group correctly… However, when I changed the contact in Nagios to e-mail a new mail-enabled security group with universal scope, the notifications stopped working. The MTA on the Nagios box, Postfix, was not getting any ‘bounce’ messages from the Exchange server. As far as Postfix was concerned, the message was being delivered. I turned on verbose logging on the hub transport receive connector and verified that the Exchange server was indeed telling the MTA that it had queued the message for delivery. After several minutes of Googling and head scratching I learnt that by default, distribution groups (security or otherwise) don’t accept mail from unauthenticated users. Whilst I thought I had successfully configured the Nagios box to perform TLS authentication, it wasn’t working correctly (the hub transport receive connector log alerted me to this). To resolve this issue, I simply allowed unauthenticated users to deliver mail to the distribution group.

To allow a distribution group to accept mail from unauthenticated users:

  1. Open Exchange Management Console.
  2. Locate the distribution group in question under Recipient Configuration.
  3. Right-click on the group and click Properties.
  4. Click on the Mail Flow Settings tab.
  5. Select the Mail Delivery Restrictions option and click the Properties button.
  6. In the Mail Delivery Restrictions dialog box, uncheck ‘Require that all senders are authenticated’ and click OK on any open dialog boxes to save changes.
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