This guide presents commands that can be executed to test a connection or a network and thus specify the source of a potential error.

Perform a Telnet...

TELNET allows you to test the connection to a server without considering all the additional settings of a mail or FTP application in order to determine the origin of a problem. If the connection does not go through on an SMTP server, for example, you will need to check if your firewall is not blocking port 587 or 465.

... on macOS

1. Search for Network Utility.
2. Go to the Ping, Lookup, or Traceroute tab depending on what you want to test.
3. You can also use a Terminal type application (command line interface, CLI / Command Line Interface) on your device and, depending on what you want to test, enter:
   traceroute [server]
nc [server] [port]
   Replace [server] with the server name or its IP address, same for [port]...

... on Windows

Enable Telnet if necessary.

1. Use a Terminal type application (command line interface, CLI / Command Line Interface) on your device, for example by typing Run then cmd.
2. In the window that opens, depending on what you want to test, type:
   tracert [server]
telnet [server] [port]
   Example: telnet mail.infomaniak.com 587 (allows you to test the SMTP port if your software/email client does not allow sending emails)...

... on Android

1. Use the application Simple Telnet Client which allows you to test very simply via 2 fields to fill in (for example mail.infomaniak.com and port 143 or 993)...

Perform a PING

PING allows you to know if a machine is accessible via the Internet. You can also check with this tool if you are addressing the correct machine, for example during a DNS change, by looking at the IP address obtained. It is possible to perform a ping on a domain name, a hostname or an IP address.