21 – FTP
22 – SSH
25 – SMTP (sending email)
53 – DNS (domain name service)
80 – HTTP (web server)
110 – POP3 (email inbox)
123 – NTP (Network Time Protocol)
143 – IMAP (email inbox)
443 – HTTPS (secure web server)
465 – SMTPS (send secure email)
631 – CUPS (print server)
993 – IMAPS (secure email inbox)
995 – POP3 (secure email inbox)