Detect Duplicate Customer Email

The Website Duplicate Email Detection feature prevents web store shoppers from creating duplicate customer accounts on your website. This feature detects duplicate email addresses when a customer chooses to register for an account. If a duplicate email address is detected, the customer is notified with an alert message, but the web store checkout workflow can proceed.
To set up duplicate email management for your website:

1. Enable the feature.
   1. Go to Setup > Company > Setup Tasks > Enable Features.
   2. On the Web Presence subtab, check the box next to Web Site Duplicate Email Management.
   3. Agree to the terms of service.WarningThis feature potentially allows an attacker to enter numerous test email addresses to build up a list of registered site users. The NetSuite security recommendation is to mitigate this risk by installing a CAPTCHA control or another program that slows down the registration process on your website. To enable the feature, you must agree to a Terms of Service statement that you understand and accept this risk. 
   4. Click Save.
2. Go to Setup > Company > Preferences > General Preferences.
3. Under Web Site Duplicate Email Management, select Enable Duplicate Detection.
4. Click Save.