User ID validation in Capture 12C

Hi All,

In our scenario few invoices come to Capture via Email Configuration. Email subject line consists of UserId, InvoiceNo, Invoice Date. We want to add a validation for Userid through some custom javascript. How we can do it in Capture 12.2.1.0 version? We've AD configuration, from their user id validates during login.

Any leads will be appreciated. Thanks.