Outlook client can't authenticate with Exchange Server

[luckymarble]

A few of my users trying to attach to our E-mail server from outside our office keep receiving the message "Exchange Server is Unavailable". This just started the other day, and only happens if the user is using a Cable Modem. It happens on all versions of Outlook, they all of sudden stopped authenticating to our server. I called cable company and of course they said they've done nothing. Am I missing something in the Exchange server? Anybody else having this problem? I'm using optimum online on Long Island.

Thanks for the help.
Stu

 

[joepc]

Try editing the host and lmhost files on the pcs and see if that works.

Are you using a vpn?

 

[luckymarble]

Already updated the hosts file. Can Ping exchange, and Telnet, IMAP and Pop3 work but won't authenticate when setup as connecting to MS Exchange.
Not running as VPN, just going over the public network.

Thanks for the ideas

 

[Nightwatch]

Please refer to the Knowledge Base Article:

http://support.microsoft.com/default.aspx?scid=kb;en-us;155831

Regards

Paul