EEK!

HEY LADY......LOOK OUT!!!!

Okay, on to more serious subjects. For the past several weeks, I've been having a problem with email. I have a Charter emal account that worked with both Incredimail and Outlook for years - but suddenly, I can't send any outgoing mail using either program to anything but OTHER Charter addresses. I can log in to my account online and use that to send email, but I hate that, and with the volume of attachments for business purposes that I send daily this is way too slow.
I spent an hour on the phone with Charter verifying I had the proper settings. They had no clue. (Go figure.)
I tried disabling outgoing antivirus email scanning temporarily to no avail. I have checked the firewall settings to be sure Port 25 was allowed, and finally turned off the firewall temporarily to try that....no luck.
The exact error I'm getting on Outlook when sending is this:

The message could not be sent because one of the recipients was rejected by the server. The rejected e-mail address was 'stptproduction@nrgbroadcast.com'. Subject 'test', Account: 'mail.charter.net', Server: 'mail.charter.net', Protocol: SMTP, Server Response: '550 #5.1.0 Address rejected.', Port: 25, Secure(SSL): No, Server Error: 550, Error Number: 0x800CCC79

If anyone knows how to fix this before I throw the laptop out the window, I'd be much obliged.