msmtp:tldr:02c2c

This command is using the echo command to pass a message "Hello world" as the input to the msmtp command.

msmtp is a command-line tool used to send emails from the terminal. It allows you to specify the SMTP server host, port, sender address, and recipient address.

Here's a breakdown of the command:

• echo "${Hello world}": The echo command simply displays the message inside the double quotes. In this case, it is "Hello world".
• |: The pipe symbol | is used to redirect the output of the preceding command (echo) to the input of the following command (msmtp).
• msmtp: The command to send emails using an SMTP server.
• --host=${localhost}: This option specifies the hostname of the SMTP server. ${localhost} is likely meant to be replaced with the actual hostname.
• --port=${999}: This option specifies the port number on which the SMTP server is listening. ${999} is likely intended to be replaced with the actual port number.
• --from=${from@example-org}: This option sets the sender's email address. ${from@example-org} is likely intended to be replaced with the actual sender's email address.
• ${to@example-org}: This is likely intended to be the recipient's email address. It is not prefixed with a flag like the other options, so it is treated as the recipient's address.

Overall, the command attempts to send an email with the subject "Hello world" from the sender specified to the recipient specified, using the specified SMTP server and port.