Sendmail has stopped sending mail suddenly on my Ubuntu machine./etc/init.d/sendmail statusMSP: is run via cron (20m)MTA: 5425 /usr/sbin/sendmail-mta -Am -L sm-mta -bd -q10mUID        PID  PPID  C STIME TTY          TIME CMDroot      5425     1  0 13:55 ?        00:00:00 sendmail: MTA: accepting connectionsDaemon Status: (process 5652) Console socket childCurrent number of children: 0QueueDir free disk space (in blocks): 43317944Load average: 0Child Process 5425 Status: accepting connectionsQUE: Same as MTAsendmail -bp /var/spool/mqueue (1 request)-----Q-ID----- --Size-- -----Q-Time----- ------------Sender/Recipient-----------v6OLnfaa027639*    2076 Mon Jul 24 21:49 <emailaddress>                 (Deferred: Connection timed out with gmaiil.com.)                                         <banks.concepcion@gmaiil.com>                Total requests: 1mail.log fileJul 25 09:16:35 localhost sm-mta[6362]: v6P9GYtm006360: v6P9GZtm006362: DSN: Service unavailableJul 25 09:16:35 localhost sm-mta[6362]: STARTTLS=client, relay=aspmx.l.google.com., version=TLSv1/SSLv3, verify=FAIL, cipher=ECDHE-RSA-AES128-GCM-SHA256, bits=128/128Jul 25 09:16:36 localhost sm-mta[6362]: v6P9GZtm006362: to=<emailaddress>, delay=00:00:01, xdelay=00:00:01, mailer=esmtp, pri=30000, relay=aspmx.l.google.com. [IPv6:2607:f8b0:400e:c00::1a], dsn=5.0.0, stat=Service unavailableJul 25 09:16:36 localhost sm-mta[6362]: v6P9GZtm006362: to=MAILER-DAEMON, delay=00:00:01, mailer=local, pri=30000, dsn=5.1.1, stat=User unknownJul 25 09:16:36 localhost sm-mta[6362]: v6P9GZtm006362: to=postmaster, delay=00:00:01, mailer=local, pri=30000, dsn=5.1.1, stat=User unknownJul 25 09:16:36 localhost sm-mta[6362]: v6P9GZtm006362: v6P9GZtn006362: return to sender: User unknownJul 25 09:16:36 localhost sm-mta[6362]: v6P9GZtn006362: to=MAILER-DAEMON, delay=00:00:00, mailer=local, pri=0, dsn=5.1.1, stat=User unknownJul 25 09:16:36 localhost sm-mta[6362]: v6P9GZtm006362: Saved message in /var/lib/sendmail/dead.letterJul 25 09:19:33 localhost sendmail[6488]: My unqualified host name (localhost) unknown; sleeping for retryJul 25 09:19:58 localhost sendmail[6507]: My unqualified host name (localhost) unknown; sleeping for retryJul 25 09:20:01 localhost sm-msp-queue[6537]: My unqualified host name (localhost) unknown; sleeping for retryJul 25 09:20:58 localhost sendmail[6507]: unable to qualify my own domain name (localhost) -- using short nameJul 25 09:20:58 localhost sendmail[6507]: gethostbyaddr(172.17.42.1) failed: 1Jul 25 09:21:01 localhost sm-msp-queue[6537]: unable to qualify my own domain name (localhost) -- using short nameUser log file error... while talking to gmail-smtp-in.l.google.com.:>>> DATA<<< 550-5.7.1 [2600:3c01::f03c:91ff:fe89:1239] 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/?p=IPv6AuthError for more information<<< 550 5.7.1 . a70si1457744pli.708 - gsmtp554 5.0.0 Service unavailable
suddenly mail is stop working for linode
email;sendmail