Our system has detected that this message is likely unsolicited mail. To reduce the amount of spam sent to Gmail,

In this case we need to study our name server and mx and etc by using following sites

Test1
Test2

Here I'm getting two warning in my ns

Different subnets

WARNING: Not all of your nameservers are in different subnets

Different autonomous systems

WARNING: Single point of failure

and one more SOA

SOA EXPIRE

Your SOA EXPIRE number is: 172800. That is NOT OK

first we can test our mail report go to the site https://www.mail-tester.com

1. copy the test mail address
2. put test mail to the address
3. get back mail-tester test the report

based on that troubleshoot our issues

we can create spf and dkim records inside the whm