Public addresses (gmail, hotmail, yahoo, etc.) should be distinguished from business addresses (with a private domain name such as @ sendinblue.com).
It is more complicated to deliver emails sent to business addresses because of firewalls and other security settings. Each company, administration or community has the ability to set a strong filtering of incoming emails, which makes it more difficult to deliver emails in inbox.
An alternative is to ask your customers to add your sender to their contacts and "" whitelister "" your IP 220.127.116.11 "