A domain name can be blacklisted for a number of reasons, including:
1. Spam complaints: If your emails are being rejected or unsubscribed from by too many people.
2. Sending too many emails: If you send too many emails per day, or without enough time between them.
3. Sending identical emails: If you send similar emails without personalization.
4. Poorly sourced email prospects: If you have a high bounce rate because of poorly sourced email prospects.
5. Suspicious activity: If your domain is involved in suspicious activity.
6. Phishing: If your domain is involved in phishing.
7. Sending emails to spam traps: If you send emails to spam traps.
8. Improper server settings: If your server settings are incorrect.
9. Issues with email headers, content, or the from address: If there are issues with your email headers, content, or the from address.
10. Possible malware on your own server.