An embedded link in an email can cause your computer to try authenticating to a remote server. A remote server might then capture your computers authentication attempt and use the resulting resulting information to find your password hash and begin cracking it. Microsoft enabled this new default around Internet Explorer version 4 or 5 to this day. It involves including an embedded link with the following format: file:///// . For example, file://:////contoso.com/index.html/.”]
Source: https://www.csoonline.com/article/3333916/i-can-get-and-crack-your-password-hashes-from-email.html