Throw exception on email or sms api limits.

application/src/main/java/org/thingsboard/server/service/mail/DefaultMailService.java

@@ -250,6 +250,8 @@ public class DefaultMailService implements MailService {
             helper.setText(body);
             mailSender.send(helper.getMimeMessage());
             apiUsageClient.report(tenantId, ApiUsageRecordKey.EMAIL_EXEC_COUNT, 1);
+        } else {
+            throw new RuntimeException("Email sending is disabled due to API limits!");
         }
     }
 

application/src/main/java/org/thingsboard/server/service/sms/DefaultSmsService.java

@@ -106,6 +106,8 @@ public class DefaultSmsService implements SmsService {
                     apiUsageClient.report(tenantId, ApiUsageRecordKey.SMS_EXEC_COUNT, smsCount);
                 }
             }
+        } else {
+            throw new RuntimeException("SMS sending is disabled due to API limits!");
         }
     }