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

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

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.

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