How to fix my email being marked as spam

All of a sudden the email I send is getting delivered to my contacts spam folders. How do I fix getting marked as spam?

Which email service do you use? Do you have your own domain name?

If you run your own mail server can you check it's sender score or post your mail server IP address so we can help you with the reputation check?

Do you have SPF & DKIM configured correctly?

Can you post the full email headers from an email that delivered to the spam folder?