I am using Jenkins in conjunction with the Active Directory plugin, so users can login with their normail domain password.
The users in Jenkins appear with the name from the AD (so the full name, with spaces etc.) and they don't have an email address.
When setting email-ext to send an email to requestors of buils, it is still using the full name rather than the ID to generate an email.
If this is by design then I would suggest an improvement in checking that the email is at least valid and try generate one with the Jenkins id + suffix.
The error I get is:
Sending to requester
Failed to send e-mail to <name here> because no e-mail address is known, and no default e-mail domain is configured