This error happens when a connection is started (and working), but then closed by the other side of things before the SMTP conversation is completed. This can also be caused by a firewall in between you and the server that might be "proxying" the SMTP conversation, and then terminates it.

There are several common reasons:

• The wrong SMTP server was specified (Edit -> Options, Email). Check your email client to see what it's using for an SMTP server, or talk to your system administratory.
• There is a firewall or antivirus package running that's aborting the SMTP conversation. This might be something running on your machine (like Norton Antivirus), or some hardware firewall that does stateful inspection. If other software works, but PingPlotter/MultiPing does not, then it's probably local to your machine - something that is filtering by which application is sending data.
• There might be something wrong with the SMTP server. Try using another email client and make sure the same SMTP server works with that.