You can't leave a Windows domain in the ProxySG appliance Management Console because the Leave button is grayed out.

To resolve the issue:

1. Identify the domain name (in this example, ‘mydomain’ is the domain name). In the Management Console, select Configuration > Authentication > Windows Domain. 
2. Leave the domain through the Command Line Interface (CLI). Enter the following in the CLI:
   
   ProxySG#config t
ProxySG#(config)security windows-domain
ProxySG#(config security windows-domains)leave mydomain
   
   If an error appears and you cannot leave the domain, troubleshoot the issue. Proceed to step 3 below if you receive the following error:
   % Domain alias "mydomain" is referenced by another configuration - check MAPI Proxy or IWA Direct Realm.


3. Check the MAPI proxy and verify if ‘mydomain’ is displayed as Exchange domain name alias:

ProxySG#config t
ProxySG#(config)mapi
ProxySG#(config mapi)view


4. If Exchange domain name alias shows the domain name, clear the settings forthe  Exchange domain alias (disassociate MAPI from Exchange domain):
   
   ProxySG#config t
ProxySG#(config)mapi
ProxySG#(config mapi) no exchange-domain


5. Refresh the Management Console (or log out and log in again). The domain should show as not joined.