Email field in VCD environment will be mapped to the Username and you cannot change it in VCD UI. VMware Cloud Director 10.6.1.1
The issue is caused because the Name identifier format will be set to Email format for your current Identity Provider.
This is a known issue with the current versions of VCD which is supposed to be resolved in the future release. We recommend you to subscribe to the article for any future updates: Subscribe to the Article
WORKAROUND: Please contact your current Identity Provider to change the Name identifier format from Email format to Default format. After doing this change you will be able to map the email correctly for the users using SAML in VCD.