Exchange 2013 - External Windows XP/Outlook 2007 Password Prompt

I have an Exchange 2013 server and everything is working correctly internal with XP clients that are connected to the domain.  My problem is that the Windows XP computers that are connecting from outside of the office that aren't connected to the domain and have local usernames and passwords keep getting the password prompts.  I put in the correct domain\username and password and it connects.  The if I close and reopen it asks me for the password, I have saved the credentials but it still asks. I have look and applied these settings from these articles but I'm still having the issue.  All of the internal and external names match my GoDaddy SSL certificate (mail.domain.com). Get-OutlookAnywhere shows:

ExternalHostname                   : mail.domain.com
InternalHostname                   : mail.domain.com
ExternalClientAuthenticationMethod : Negotiate
InternalClientAuthenticationMethod : Ntlm
IISAuthenticationMethods           : {Basic, Ntlm, Negotiate}

http://jaworskiblog.com/2013/04/13/setting-internal-and-external-urls-in-exchange-2013/

http://pickettsproblems.wordpress.com/2013/04/08/windows-xp-users-not-connecting-to-exchange-2013-server/