Hi,
We have mixed environment, where Exchange 2003 & Exchange 2007 Environment & as usual Exchange 2007 CAS Server is internet facing & its redirecting request to Exchange front end Server for those whose mailbox is still in Legacy Exchange Server.
For Exchange Server 2003 Mailbox user is facing issue while they are access their mailbox through Active sync.
Please suggest , how we to & what are the specific things I have check.
Check this..
Exchange 2003 - Activesync Connection Problems FAQ
http://www.experts-exchange.com/Software/Server_Software/Email_Servers/Exchange/A_1798-Exchange-2003-Activesync-Connection-Problems-FAQ.html
Hope that helps :)