I have no experience with Citrix or MDaemon but, after taking a look at some info on them, I'm inclined to think you've got an unnecessarily complex setup there with the combination of Citrix, MDaemon, and Exchange.
Here's a quote from
http://www.altn.com/Products/MessagingSolutions/MDaemon/ : "Outlook users can share Calendar, Task, Contact, Notes, and Journal folders without the expense or expertise required by Microsoft Exchange Server." This implies that MDaemon is an alternative to Exchange. So, why are you using both?
What version of Windows are you using and what version of Citrix? This reference,
For: Access Gateway Standard Edition and Access Gateway Advanced Edition, Version 4.5, says,
Known Issues for this Release 1. After installing the beta Secure Access Client on Windows Vista, the client computer might not be able to connect to network resources. If this happens, uninstall the beta Secure Access Client, restart the client computer, and then install the beta Secure Access Client again.
So, I think maybe you need to uninstall Citrix as a first troubleshooting step and see whether resolves the problem. Don't reinstall it until you've tried doing email with it uninstalled. And, if that doesn't work, then you need to determine whether there's some conflict in using MDaemon and Exchange together.