Getting emails right into the main inbox is not an easy task specially for email providers like Google. In order to get emails into Gmail Inbox your have to follow certain rules. Please ensure following measures are taken and your email should reach the Gmail Inbox fine.
- Install SSL on your domain
- Ensure RDNS on your server hostname
- Ensure SPF
- Ensure DKIM
- Test Your email at https://www.mail-tester.com
- Register your domain on https://postmaster.google.com/u/0/managedomains
- Ensure your ip not blacklisted. Better to add your server ip on https://hetrixtools.com/
Your good to go now. Also note that if you are listed on black list specailly Spamhaus then your emails wont get into Gmail Inbox or Live inbox. You might have to add your ip manually to whitelits using some email providers like outlook.