Sendmail Cannot Deliver to Gmail – IPv6 Sending Guidelines

gmailipv6sendmail

I am having trouble in delivering mail to google from a fresh sendmail install on ubuntu 14.04. The DNS-records seem to be fine for the ip. Something else must be wrong.

Sending mail from command line: 

sudo sendmail -v -Am -i myname@gmail.com;

Verbose output:

myname@fx1:/etc/mail$ sudo sendmail -v -Am -i myname@gmail.com;
myname@gmail.com... Connecting to aspmx.l.google.com. via esmtp...
220 mx.google.com ESMTP v1si55415385wja.21 - gsmtp
>>> EHLO staging.mydomain.com
250-mx.google.com at your service, [2a01:4f8:212:27c8::2]
250-SIZE 35882577
250-8BITMIME
250-STARTTLS
250-ENHANCEDSTATUSCODES
250-PIPELINING
250-CHUNKING
250 SMTPUTF8
>>> STARTTLS
220 2.0.0 Ready to start TLS
>>> EHLO staging.mydomain.com
250-mx.google.com at your service, [2a01:4f8:212:27c8::2]
250-SIZE 35882577
250-8BITMIME
250-ENHANCEDSTATUSCODES
250-PIPELINING
250-CHUNKING
250 SMTPUTF8
>>> MAIL From:<myname@staging.mydomain.com>
250 2.1.0 OK v1si55415385wja.21 - gsmtp
>>> RCPT To:<myname@gmail.com>
>>> DATA
250 2.1.5 OK v1si55415385wja.21 - gsmtp
354  Go ahead v1si55415385wja.21 - gsmtp
>>> .
550-5.7.1 [2a01:4f8:212:27c8::2] Our system has detected that this message does
550-5.7.1 not meet IPv6 sending guidelines regarding PTR records and
550-5.7.1 authentication. Please review
550-5.7.1  https://support.google.com/mail/?p=ipv6_authentication_error for more
550 5.7.1 information. v1si55415385wja.21 - gsmtp
myname... Connecting to local...
myname... Sent

Any help is greatly apreciated. Thank you in advance.

Best Answer

From Google's point of view, they are trying to verify the identity of the IP address connecting to them, so they will attempt to look up the PTR record for 2a01:4f8:212:27c8::2.

When they resolve that to staging.findix.com, they will then attempt to check that this resolves back to 2a01:4f8:212:27c8::2 - which it doesn't - see this lookup result.

Reverse (PTR record) Lookup

cwatson@thor:~$ nslookup 31.220.4.52
Server:     127.0.0.1
Address:    127.0.0.1#53

Non-authoritative answer:
52.4.220.31.in-addr.arpa    name = tyr.vikingserv.net.

Forward (A record) Lookup

cwatson@thor:~$ nslookup tyr.vikingserv.net
Server:     127.0.0.1
Address:    127.0.0.1#53

Non-authoritative answer:
Name:   tyr.vikingserv.net
Address: 31.220.4.52
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