Hi Steve, We ran into this a few weeks back. Assuming you are not using native IPv6 in your environment what is happening is Exchange is putting the local link IPv6 address of the server into the message header. Google checks this and sees it’s not a proper native IPv6 address and blocks the message. The fix for us was to disable IPv6 in the registry on our Exchange server until we are ready to go to true IPv6. See the "for more information" section at this link http://support.microsoft.com/kb/929852 After making the registry change and rebooting the IPv4 address was showing in the message headers and google allowed mail normally. Proceed with caution though as others online have ran into issues after disabling IPv6, also from what I have read DO NOT uncheck IPv6 on the network adapter as the registry is the proper place. [MSU Helmet]<http://> Josh Rush Server/Network Administrator Advancement Information Systems & Donor Strategy Michigan State University University Advancement 535 Chestnut Road, Room 300 East Lansing, MI 48824-3482 Direct: 517-884-2501 Office Fax: 517-884-1219 Visit us at http://advancement.msu.edu/ Was this interaction helpful? Please fill out our quick AIS-DS customer survey<https://aisdsbox.advancement.msu.edu/Lists/Customer%20Survey/newSurvey.aspx?Source=https://aisdsbox.advancement.msu.edu/Pages/Survey-Thank-You.aspx>. The information contained in this e-mail may be confidential and is intended solely for the use of the named addressee. Access, copying, or re-use of the e-mail or any information contained therein by any other person is not authorized. If you are not the intended recipient please notify us immediately by returning the e-mail to the originator. -----Original Message----- From: Steven M. Plemmons [mailto:[log in to unmask]] Sent: Wednesday, March 19, 2014 4:20 PM To: [log in to unmask] Subject: [MSUNAG] Google Blocking E-mail - IPv6 error Suddenly, google is blocking messages sent from our exchange server to gmail addresses. The following error message is given. Is anyone else seeing this? Thanks, Steve Plemmons Systems Analyst II/S Department of Mathematics Michigan State University 619 Red Cedar Road C339 Wells Hall Office: 517-353-4673 [log in to unmask] mx.google.com gave this error: [2002:2308:4821::2308:4821] Our system has detected that this message does not meet IPv6 sending guidelines regarding PTR records and authentication. Please review https://support.google.com/mail/?p=ipv6_authentication_error for more information. l7si4236735icq.11 - gsmtp Your message wasn't delivered due to a permission or security issue. It may have been rejected by a moderator, the address may only accept e-mail from certain senders, or another restriction may be preventing delivery.