If you want to connect to citrix from outisde the office through your firewall then the citrix server needs configuring for an alternate connection. Here is a guide on how to setup citrix for external connections.
You can block applications on your network from being run with something called a hash rule, these can be deployed with group policy. Here is a step by step guide on blocking applications on your network.
How to renew your expired exchange 2007 certificate.A guide on How To Remove An Expired Exchange 2007 Certificate and Create A New Certificate. This needs to be done every so often when your exchange certificates expire.