Where does workflow gets email information from?

In workflow, orders gets sent to people's email for approval and such. When create user in EBS, system administrator->security->user->define The email address linked to user was correct. However, in the email system we constantly getting email undeliverable messages where the email address for the user is way off. Is there anywhere else that EBS system is looking for email addresses?

We are using EBS version 12.1.3

For example, in the create user screen, the email address entered was user@psd.company.com.

But mail delivery system from the ebs server will send out message says:

The following message to