As mentioned before, check the mail-logs at your webserver, you'll find this "authentication required" message logged there as response to the hotmail servers trying to relay mail to that webserver.
At 23-10-2012 14:49, Suresh Ramasubramanian wrote: > "authentication required" is a bizzarre error to return. > > Does it go away if you actually turn off graylisting for hotmail? > > On Tuesday, October 23, 2012, Carlos M. Perez wrote: > >> Mike, >> >> I think this is exactly what is going on. The domains that are having >> issues have greylisting on with the spam filtering service and are >> hosted on a farm of hosting servers. We have blocked port 25 on the >> main hosting IP of the web server, and moved the built in mail server to >> listen on another IP. This appears to be working, or at least has been >> for almost 12 hours. >> >> The real question is why is hotmail/live the only system that apparently >> does this; which seems to be in contradiction to RFC, and how everyone >> else does it. The one thing that MS chooses to be different with... >> >> Thanks, >> >> Carlos M. Perez >> Runcentral, LLC >> >> On 10/23/2012 4:28 AM, Michiel Klaver wrote: >>> Carlos, >>> >>> check the mail logs of your web-server, your domain might have a primary >>> A-record pointing to something different than MX-records. When the MX >>> servers do something like greylisting and bounce with a temp-code (4xx) >>> hotmail servers will try alternative records (like @ IN A) and might >> find a >>> listening mail-daemon at your webserver. >>> >>> >>> At 23-10-2012 00:16, Carlos M. Perez wrote: >>>> 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;administra...@xxxx.com <javascript:;> >>>> Action: failed >>>> Status: 5.5.0 >>>> Diagnostic-Code: smtp;550 authentication required >>>> = >>>> >>>> Kindly contact me off-list. >>>> >>>> Thanks, >>>> >>> >>> >>> >> >> >> >> >> >> >> >> >