diff --git a/docs/installation_guide.md b/docs/installation_guide.md
index a3d5342b2..1e3824665 100644
--- a/docs/installation_guide.md
+++ b/docs/installation_guide.md
@@ -46,10 +46,10 @@ Offline installer:
 Configuration parameters are located in the file **harbor.cfg**. 
 
 There are two categories of parameters in harbor.cfg, **required parameters** and **optional parameters**.  
+
 * **required parameters**: These parameters are required to be set in the configuration file. They will take effect if a user updates them in ```harbor.cfg``` and run the ```install.sh``` script to reinstall Harbor.
-* **optional parameters**: These parameters are optional. If they are set in ```harbor.cfg```, they only take effect in the first launch of Harbor. 
+* **optional parameters**: These parameters are optional for updating, i.e. user can leave them as default and update them on Web UI after Harbor is started.  If they are set in ```harbor.cfg```, they only take effect in the first launch of Harbor. 
 Subsequent update to these parameters in ```harbor.cfg``` will be ignored. 
-The user can leave them blank and update them on Web UI after Harbor is started.  
 
     **Note:** If you choose to set these parameters via the UI, be sure to do so right after Harbor
 is started. In particular, you must set the desired **auth_mode** before registering or creating any new users in Harbor. When there are users in the system (besides the default admin user), 
@@ -69,9 +69,10 @@ The parameters are described below - note that at the very least, you will need
 * **secretkey_path**: The path of key for encrypt or decrypt the password of a remote registry in a replication policy.
 
 ##### Optional parameters
-* **Email settings**: These parameters are needed for Harbor to be able to send a user a "password reset" email, and are only necessary if that functionality is needed.  Also, do note that by default SSL connectivity is _not_ enabled - if your SMTP server requires SSL, but does _not_ support STARTTLS, then you should enable SSL by setting **email_ssl = true**.
+* **Email settings**: These parameters are needed for Harbor to be able to send a user a "password reset" email, and are only necessary if that functionality is needed.  Also, do note that by default SSL connectivity is _not_ enabled - if your SMTP server requires SSL, but does _not_ support STARTTLS, then you should enable SSL by setting **email_ssl = true**.  For a detailed description about "email_identity" please refer to [rfc2595](https://tools.ietf.org/rfc/rfc2595.txt)
   * email_server = smtp.mydomain.com 
   * email_server_port = 25
+  * email_identity = 
   * email_username = sample_admin@mydomain.com
   * email_password = abc
   * email_from = admin <sample_admin@mydomain.com>