Added a form validation check to detect typical errors like http://www.nabble.com/cannot-setup-email-account-td25727896.html

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@22378 71c3de6d-444a-0410-be80-ed276b4c234a

core/src/main/java/hudson/tasks/Mailer.java

@@ -392,6 +392,13 @@ public class Mailer extends Notifier {
             return doAddressCheck(value);
         }
 
+        public FormValidation doCheckDefaultSuffix(@QueryParameter String value) {
+            if (value.matches("@[A-Za-z0-9.\\-]+") || Util.fixEmptyAndTrim(value)==null)
+                return FormValidation.ok();
+            else
+                return FormValidation.error("This field should be '@' followed by a domain name.");
+        }
+
         /**
          * Send an email to the admin address
          * @throws IOException