You are on a shared server, and your host mail server has a REALLY sh*tty reputation due to spammers using it.
You don't have SPF, DKIM or DMARC set up.
Your email shows to be from one address, but is actually being sent from another.
As I said, the response itself tells you the issue.. there is something "spammy" with your email.
What host do you use?
How do you send email (via a regular gmail account or such)?
Have you actually configured DKIMl SPF and DMARC for your domain emails in DNS?