Question: what ports are open by default?
Answer: 20 – FTP (File Transfer Protocol)
22 – Secure Shell (SSH)
25 – Simple Mail Transfer Protocol (SMTP)
53 – Domain Name System (DNS)
80 – Hypertext Transfer Protocol (HTTP)
110 – Post Office Protocol (POP3)
143 – Internet Message Access Protocol (IMAP)
443 – HTTP Secure (HTTPS)