Domain Blacklists are real-time databases that identify domains that are known to send spam or malicious content. They are defined by ISPs (Internet Service Providers) and specialized organisms and are used as references by email servers to determine if an incoming email can be trusted or not.
Email domains that are blacklisted are likely to land in spam, as they have a history of negative behaviors.
Your domain has risks to be added to a blacklist if:
You have a high bounce rate (soft or hard) on emails you send.
You have a low engagement (open rate, answer rate, etc.) on emails you send.
You have a high proportion of emails sent that are flagged as spam by recipients.
You send emails into "Spam Traps" (inactive email addresses that are use to spot spam behavior and poor list hygiene).
Your domain is compromised, and used by spammers against your will.
Good sending practices and active authentication protocols (SPF, DKIM and DMARC) can help you to reduce the risks to have your domain blacklisted.