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

Perform a Telnet…

TELNET allows you to test the connection to a server without taking into account all the additional settings of a mail or FTP application, in order to determine the source of a problem. For example, if the connection fails on an SMTP server, you will need to check whether your firewall is 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 application (command-line interface, CLI) 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, and do the same for [port]…

… on Windows

Enable Telnet beforehand if necessary.

1. Use a Terminal application (command-line interface, CLI) 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(this allows you to test the SMTP port if your software/email client does not allow you to send emails)…

… on Android

1. Use the Simple Telnet Client app, which allows you to easily test by filling in two fields (for example, mail.infomaniak.com and port 143 or 993)…

Perform a PING

PING allows you to determine if a machine is accessible via the Internet. You can also use this tool to verify that you are connecting to the correct machine, for example, after a DNS change, by checking the IP address obtained. It is possible to perform a ping on a domain name, a hostname, or an IP address.