Simply put, FTP allows you to upload, download and copy files within a set of directories.
Sometimes it can happen that the FTP port is blocked by your company firewall. But how do you know if the firewall is really the cause of the FTP port blocking?
Check if FTP port 21 has been blocked by your ISP
In case our operating system is Windows, then:
We go to Start and then to Execute; in the window that opens, we write cmd and then press Send. We will open, in this way, a black window, called "Command Prompt" or "DOS"; we write, therefore, in this window:
telnet mydomain.com 21 , replacing mydomain.com with our domain name.
Otherwise, if we have a Apple Mac, we should go to the application directory and, more precisely, to the subfolder "Utilities"; in this subfolder we will find an application called "Terminal": let's open it and write telnet mydomain.com 21 replacing mydomain.com with our domain name) ; then we press send.
Once these simple and short steps have been carried out, we will obtain different results, depending on whether everything has been successful or not.
In case the connection went well, here are the messages that we will see:
220---------- Welcome to Pure-FTPd [privsep] [TLS] --------------
220-You are user number 5 of 50 allowed.
220-Local time is now 15:32. Server port: 21.
220-This is a private system - No anonymous login
220-IPv6 connections are also welcome on this server.
220 You will be disconnected after 15 minutes of inactivity.
If something different from these messages appears to you, then you will need to contact your ISP or network administrator (if you are in a office), asking them to unlock Port 21.