With Exchange 2013 administration moving to browser based, you can manage your Exchange 2013 environment from anywhere in the world, provided that they are published. How can we switch off access from outside the corporate network?
You can manage your 2013 environment with EAC internally by navigating to https://casserver/ecp or https://loadbalancedurl/ecp if you have an NLB or load balancer in place. Your external webmail url (https://mail.domain.com) can be used to access the EAC (with /ecp) from outside the corporate network.
You may have a valid reason to turn off access to EAC from outside the internal network and the good thing is that it can be turned off, without affecting your OWA or OWA Options. By default, the EAC access from outside the network is enabled.
--> Please see the rest on the blog : http://www.howexchangeworks.com/2012/11/turn-off-internet-access-to-exchange-2013-eac.html