Que signifie this is the mail system at host mwinf5d71.orange.fr

A nice technical question!

"This is the mail system at host mwinf5d71.orange.fr" is a message that is typically sent by a mail server (also known as a mail transfer agent or MTA) when it receives an email message that it cannot deliver to its intended recipient.

Here's what it means:

• "This is the mail system at host": This is a message from the mail server that is responsible for delivering the email message.
• "mwinf5d71.orange.fr": This is the hostname or domain name of the mail server that is sending the message. In this case, it appears to be a mail server operated by Orange, a French telecommunications company.

When a mail server receives an email message, it checks the recipient's email address to see if it can deliver the message to that address. If it cannot deliver the message (e.g., because the recipient's email address does not exist or is not valid), the mail server will send a "bounce" message back to the sender, which is what this message is.

The bounce message is usually sent to the sender's email address and includes information about why the message could not be delivered. In this case, the message is simply stating that it is the mail system at the specified host (mwinf5d71.orange.fr) that is responsible for delivering the message, but it cannot do so.

So, in summary, this message is a technical notification from a mail server indicating that it cannot deliver an email message to its intended recipient.