Unable to Send Email! - Time Warner Internet

This question is about "Unable to Send Email!", with Time Warner Cable internet and apps. I'm trying to help my mother, who has been unable to send email for about a week. Prior to that everything worked fine, and no changes have been made to account for the unexpected behavior.

The error message via Thunderbird says... "An error occured while sending mail: The Mail server sent an incorrect greeting: p-impout010.msg.pkvw.co.charter.net cmsmtp blocked AUP#CMDNS"

So I installed eMClient, to see if it would resolve things. Nope; it gives a similar error... "Invalid server reply when connecting: 'p-impout002.msg.pkvw.co.charter.net cmsmtp blocked AUP#CMDNS"

What in the world is going on and how can we fix it???

Unable to Send Email!?