Disabling 6to4 and Teredo

 •I have recently started seeing an issue where Google's Spam servers was rejecting emails with the following error
mx.google.com rejected your message to the following e-mail addresses: mx.google.com gave this error: 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/answer/81126 for more information. a48si4416825yhd.402 - 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. mx.google.com #550-5.7.1 Our system has detected that this 550-5.7.1 message does not meet IPv6 sending guidelines regarding PTR records 550-5.7.1 and authentication. Please review 550 5.7.1 https://support.google.com/mail/answer/81126 for more information. a48si4416825yhd.402 - gsmtp ##
However our servers were not using ipv6 but Windows tries to use 6to4 and Teredo automatically, not always resulting in a good IPv6 experience. To disable both, execute these commands: netsh interface ipv6 6to4 set state disabled netsh interface teredo set state disabled On Windows XP teredo isn’t a context inside interface, but rather a setting in ipv6: netsh interface ipv6 set teredo disabled of course the recommended solution is to properly setup ipv6 but this can tide you over in the mean time.

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