Sendgrid integration for Google Cloud Instance(Centos7)

I am setting up a Website for my Business over Google Cloud Engine and I am trying to integrate with the SendGrid. I am not able to successfully send the Emails even after following the integration steps mentioned in the Google and SendGrid Documentation. [login to view URL] [login to view URL] [login to view URL] When I try to send the Email, I have the logs pointed out that it is getting bounced! [root@mail ~]# echo 'Test passed.' | mail -s Test-Email talk2hosur@[login to view URL] [root@mail ~]# tail -f /var/log/maillog Dec 2 16:44:13 mail postfix/pickup[28706]: 0CB988722C6: uid=0 from=<root> Dec 2 16:44:13 mail postfix/cleanup[28957]: 0CB988722C6: message-id=<20171202164413.0CB988722C6@[login to view URL]> Dec 2 16:44:13 mail postfix/qmgr[28707]: 0CB988722C6: from=<root@[login to view URL]>, size=448, nrcpt=1 (queue active) Dec 2 16:44:13 mail postfix/error[28959]: 0CB988722C6: to=<talk2hosur@[login to view URL]>, relay=none, delay=0.04, delays=0.02/0.01/0/0.01, dsn=5.0.0, status=bounced ([[login to view URL]]:2525) Dec 2 16:44:13 mail postfix/cleanup[28957]: 142BB8063A8: message-id=<20171202164413.142BB8063A8@[login to view URL]> Dec 2 16:44:13 mail postfix/qmgr[28707]: 142BB8063A8: from=<>, size=2205, nrcpt=1 (queue active) Dec 2 16:44:13 mail postfix/bounce[28960]: 0CB988722C6: sender non-delivery notification: 142BB8063A8 Dec 2 16:44:13 mail postfix/qmgr[28707]: 0CB988722C6: removed Dec 2 16:44:13 mail postfix/local[28961]: 142BB8063A8: to=<root@[login to view URL]>, relay=local, delay=0.02, delays=0/0.01/0/0, dsn=2.0.0, status=sent (delivered to mailbox) Dec 2 16:44:13 mail postfix/qmgr[28707]: 142BB8063A8: removed Postfix configurationfile [login to view URL] Note : Need a proper documentation about the fix for this project to have the amount paid.