Sendmail письмо отправляется,но не доходит.Что не так?

root@server:~# echo "mail" | sendmail -v mail@gmail.com
mail@gmail.com... Connecting to [127.0.0.1] via relay...
220 localhost.localdomain ESMTP Sendmail 8.14.4/8.14.4/Debian-2ubuntu2.1; Wed, 21 Mar 2018 12:05:39 GMT; (No UCE/UBE) logging access from: localhost.localdomain(OK)-localhost.localdomain [127.0.0.1]
>>> EHLO localhost.localdomain
250-localhost.localdomain Hello localhost.localdomain [127.0.0.1], pleased to meet you
250-ENHANCEDSTATUSCODES
250-PIPELINING
250-EXPN
250-VERB
250-8BITMIME
250-SIZE
250-DSN
250-ETRN
250-AUTH DIGEST-MD5 CRAM-MD5
250-DELIVERBY
250 HELP
>>> VERB
250 2.0.0 Verbose mode
>>> MAIL From:<root@localhost.localdomain> SIZE=46 AUTH=root@localhost.localdomain
250 2.1.0 <root@localhost.localdomain>... Sender ok
>>> RCPT To:<mail@gmail.com>
>>> DATA
250 2.1.5 <mail@gmail.com>... Recipient ok
354 Enter mail, end with "." on a line by itself
>>> .
050 <mail@gmail.com>... Connecting to gmail-smtp-in.l.google.com. via esmtp...
050 220 mx.google.com ESMTP c77-v6si1537205lfg.297 - gsmtp
050 >>> EHLO localhost.localdomain
050 250-mx.google.com at your service, [2a00:1838:37:14d::ba67]
050 250-SIZE 157286400
050 250-8BITMIME
050 250-STARTTLS
050 250-ENHANCEDSTATUSCODES
050 250-PIPELINING
050 250-CHUNKING
050 250 SMTPUTF8
050 >>> STARTTLS
050 220 2.0.0 Ready to start TLS
050 >>> EHLO localhost.localdomain
050 250-mx.google.com at your service, [2a00:1838:37:14d::ba67]
050 250-SIZE 157286400
050 250-8BITMIME
050 250-ENHANCEDSTATUSCODES
050 250-PIPELINING
050 250-CHUNKING
050 250 SMTPUTF8
050 >>> MAIL From:<root@localhost.localdomain> SIZE=341
050 250 2.1.0 OK c77-v6si1537205lfg.297 - gsmtp
050 >>> RCPT To:<mail@gmail.com>
050 >>> DATA
050 250 2.1.5 OK c77-v6si1537205lfg.297 - gsmtp
050 354  Go ahead c77-v6si1537205lfg.297 - gsmtp
050 >>> .
050 550-5.7.1 [2a00:1838:37:14d::ba67] Our system has detected that this message
050 550-5.7.1 does not meet IPv6 sending guidelines regarding PTR records and
050 550-5.7.1 authentication. Please review
050 550-5.7.1  https://support.google.com/mail/?p=IPv6AuthError for more information
050 550 5.7.1 . c77-v6si1537205lfg.297 - gsmtp
050 <root@localhost.localdomain>... Connecting to local...
050 <root@localhost.localdomain>... Sent
250 2.0.0 w2LC5dvA001979 Message accepted for delivery
mail@gmail.com... Sent (w2LC5dvA001979 Message accepted for delivery)
Closing connection to [127.0.0.1]
>>> QUIT
221 2.0.0 localhost.localdomain closing connection
You have new mail in /var/mail/root