On a Plesk server, you need to open specific ports in the firewall to ensure the proper functioning of various services. The necessary ports may vary depending on the services you have enabled and the specific requirements of your server. Here are the most common ports that may need to be opened on a Plesk server:

1. HTTP (TCP port 80):

   • Used for regular unencrypted web traffic.

2. HTTPS (TCP port 443):

   • Used for encrypted web traffic over SSL/TLS.

3. FTP (TCP ports 20 and 21):

   • Port 20 is used for data transfer (active mode), while port 21 is used for control.

4. SSH (TCP port 22):

   • Used for secure shell access for remote server management.

5. SMTP (TCP port 25):

   • Used for sending email messages.

6. SMTPS (TCP port 465):

   • Used for encrypted SMTP connections over SSL.

7. Submission (TCP port 587):

   • Used for email submission by mail clients.

8. IMAP (TCP port 143):

   • Used for email retrieval by mail clients.

9. IMAPS (TCP port 993):

   • Used for encrypted IMAP connections over SSL.

10. POP3 (TCP port 110):

    • Used for email retrieval by mail clients.

11. POP3S (TCP port 995):

    • Used for encrypted POP3 connections over SSL.

12. DNS (UDP port 53):

    • Used for domain name resolution.

13. Plesk Control Panel (TCP port 8443):

    • Used for secure access to the Plesk control panel.

14. MySQL/MariaDB (TCP port 3306):

    • Used for database connections.

15. PostgreSQL (TCP port 5432):

    • Used for PostgreSQL database connections.

16. Webmail (TCP port 7080 or 7081):

    • Used for webmail access if enabled.

17. Plesk File Manager (TCP port 8447):

    • Used for secure access to the Plesk File Manager.

18. WebDav (TCP port 8880 or 7081):

    • Used for WebDav access if enabled.

19. Node.js (TCP port 3000):

    • Used for Node.js applications if enabled.

20. Joomla Toolkit (TCP port 10101):

    • Used for Joomla Toolkit if enabled.

Remember to adjust these recommendations based on your specific configuration and requirements. If you're not sure which ports need to be open, consult Plesk's documentation or contact your hosting provider for guidance. Additionally, always apply best practices for firewall security and consider using tools like fail2ban for additional protection against unauthorized access attempts.