To see a complete list of servers ports and what they connect to see:
A server, particularly one running Linux, has a standard set of ports that are configured to operate with certain applications.
Here are some of the default Linux ports available on most servers, listed in no particular order.
80 – This is probably the most essential port on a web hosting server since all websites use it, whether you have one or one thousand. It is the standard HTTP port on all servers
443 – Anytime someone connects to your site with HTTPS, they will use port 443. It is the default port for encrypted sites.
25 – When a mail server, such as Sendmail sends email, this is the port it uses by default. Changing it may be a serious consideration if your ISP blocks port 25 in an attempt to derail spammers.
110 – Incoming mail from a POP3 mail server will use port 110.
143 – Incoming mail that relies on IMAP instead of POP3, will use this port.
3306 – The port MySQL uses to connect to remote clients. If you manipulate your databases directly on the server, it is best to configure your firewall to keep this port closed.
21 – The standard port used for File Transfer Protocol (FTP).
22 – The standard port used for Secure Shell / SSH
There are other possible ports you may use, such as control panels, game servers, and instant messaging. Check the specific software’s documentation for more information.