Index: src/main/java/org/wso2/carbon/core/services/authentication/AuthenticationFailureException.java
===================================================================
--- src/main/java/org/wso2/carbon/core/services/authentication/AuthenticationFailureException.java	(revision 141175)
+++ src/main/java/org/wso2/carbon/core/services/authentication/AuthenticationFailureException.java	(working copy)
@@ -27,7 +27,8 @@
     public enum AuthenticationFailureReason {
         INVALID_USER_NAME,
         INVALID_PASSWORD,
-        SYSTEM_ERROR
+        SYSTEM_ERROR,
+        RESERVED_TENANT_DOMAIN,
     }
 
     private AuthenticationFailureReason authenticationFailureReason;
@@ -65,6 +66,10 @@
             return "Authentication failed - System error occurred. Please check server logs for more details.";
         }
 
+        if (authenticationFailureReason == AuthenticationFailureReason.RESERVED_TENANT_DOMAIN) {
+            return "Authentication failed - System error occurred. Tenant domain name is reserved.";
+        }
+
         throw new RuntimeException("Un-identified authentication failure reason");
 
     }
Index: src/main/java/org/wso2/carbon/core/services/authentication/AuthenticationAdmin.java
===================================================================
--- src/main/java/org/wso2/carbon/core/services/authentication/AuthenticationAdmin.java	(revision 141175)
+++ src/main/java/org/wso2/carbon/core/services/authentication/AuthenticationAdmin.java	(working copy)
@@ -82,6 +82,16 @@
                 return false;
             }
 
+            String domainNameFromUserName = CarbonAuthenticationUtil.extractTenantDomain(username);
+            if (domainNameFromUserName != null &&
+                domainNameFromUserName.equals(MultitenantConstants.SUPER_TENANT_DOMAIN_NAME)) {
+                if (log.isDebugEnabled()) {
+                    log.debug("Authentication Failure..Provided tenant domain name is reserved..");
+                }
+                throw new AuthenticationFailureException(
+                        AuthenticationFailureException.AuthenticationFailureReason.RESERVED_TENANT_DOMAIN,
+                        username);
+            }
             if (remoteAddress != null) {
                 AuthenticationUtil.validateRemoteAddress(remoteAddress);
             } else {
Index: src/main/java/org/wso2/carbon/core/services/authentication/AbstractAuthenticator.java
===================================================================
--- src/main/java/org/wso2/carbon/core/services/authentication/AbstractAuthenticator.java	(revision 141175)
+++ src/main/java/org/wso2/carbon/core/services/authentication/AbstractAuthenticator.java	(working copy)
@@ -25,6 +25,7 @@
 import org.osgi.framework.BundleContext;
 import org.osgi.util.tracker.ServiceTracker;
 import org.wso2.carbon.CarbonConstants;
+import org.wso2.carbon.base.MultitenantConstants;
 import org.wso2.carbon.core.AbstractAdmin;
 import org.wso2.carbon.core.common.AuthenticationException;
 import org.wso2.carbon.core.security.AuthenticatorsConfiguration;
@@ -95,7 +96,16 @@
             throw new AuthenticationFailureException
                     (AuthenticationFailureException.AuthenticationFailureReason.INVALID_USER_NAME);
         }
-
+        String domainNameFromUserName = CarbonAuthenticationUtil.extractTenantDomain(userNameInRequest);
+        if (domainNameFromUserName != null && domainNameFromUserName.equals(
+                MultitenantConstants.SUPER_TENANT_DOMAIN_NAME)) {
+            if (log.isDebugEnabled()) {
+                log.debug("Authentication Failure..Provided tenant domain name is reserved..");
+            }
+            throw new AuthenticationFailureException(
+                    AuthenticationFailureException.AuthenticationFailureReason.RESERVED_TENANT_DOMAIN,
+                    userNameInRequest);
+        }
         RealmService realmService;
         try {
             realmService = getRealmService();
Index: src/main/java/org/wso2/carbon/core/services/util/CarbonAuthenticationUtil.java
===================================================================
--- src/main/java/org/wso2/carbon/core/services/util/CarbonAuthenticationUtil.java	(revision 141175)
+++ src/main/java/org/wso2/carbon/core/services/util/CarbonAuthenticationUtil.java	(working copy)
@@ -223,4 +223,12 @@
                 new LoginAttempt(username, tenantId, remoteAddress, new Date(), true, null);
         LoginStatDatabase.recordLoginAttempt(loginAttempt);
     }
+
+    public static String extractTenantDomain(String userName){
+        if (userName.contains("@")) {
+            String tenantDomain = userName.substring(userName.lastIndexOf('@') + 1);
+            return tenantDomain;
+        }
+        return null;
+    }
 }