Hi, We're trying to resolve some delivery issues reported by hotmail users. Started happening a few weeks ago. Getting immediate NDRs, and the server that is supposed to receive the email has no records of attempts. The messages also don't match what the receiving server should be sending. The server(s) listed in the MX should receive all email without authentication, since it's a mail filtering service (Maxmail) === Reporting-MTA: dns;snt0-omc3-s27.snt0.hotmail.com Received-From-MTA: dns;SNT133-W53 Arrival-Date: Mon, 22 Oct 2012 14:09:49 -0700 Final-Recipient: rfc822;administrator@xxxx.com Action: failed Status: 5.5.0 Diagnostic-Code: smtp;550 authentication required === Kindly contact me off-list. Thanks, -- Carlos M. Perez Runcentral, LLC