email error

[CarbonTerry]

I have made a website for a friend and have configured the outlook Express for several employees. All is well unti today. No outgoing email from any computer (7). Could this be a website problem or something outside the site? Maybe impossible to tell?
The complete website is not posted, only a test for the index page.
www.masterpac.com

[CarbonTerry]

Re: email error

Here's the error message

The message could not be sent because one of the recipients was rejected by the server. The rejected e-mail address was 'jim@masterpac.com'. Subject 'test 10:30', Account: 'mail.masterpac.com', Server: 'mail.masterpac.com', Protocol: SMTP, Server Response: '550 Connection denied after dictionary attack', Port: 25, Secure(SSL): No, Server Error: 550, Error Number: 0x800CCC79


Your server has unexpectedly terminated the connection. Possible causes for this include server problems, network problems, or a long period of inactivity. Account: 'mail.masterpac.com', Server: 'mail.masterpac.com', Protocol: SMTP, Port: 25, Secure(SSL): No, Error Number: 0x800CCC0F