Hi
Please reference this
http://www.experts-exchange.com/Software/Server_Software/Email_Servers/Exchange/Q_23121409.html--- Start cut and paste ----
In Exchange 2007 when you disable a mailbox via the ECM the mailbox attributes are removed from the user account and the mailbox is marked for deletion and moved to the disconnected mailbox area.
When you select remove it does the same as above however is also deletes the user account from AD. Therefore disabling a user seems to be a two step process now where you disable the mailbox and then disable to account.
http://www.msexchange.org/tutorials/Managing-mailboxes-Exchange-Server-2007-Part2.html--- End cut and paste ----