3665847 - All recipient addresses were invalid or no addresses were given

Use SAP Cloud Identity Service to login SAP Build Process Automation.
Create a process and add a mail notification in it, in this mail notification, set mail header "To" as "Started By"
Running the process, it failed to send mail with error:
Recipients:
To: <user>
Ignored Recipients: <user>
Error message:
All recipient addresses were invalid or no addresses were given.

It shows that the user is not identified by an email address.

All recipient addresses were invalid or no addresses were given, Started By, email, process , KBA , LOD-BPM-WFS , Workflow Service Runtime / Editor , BC-IAM-IDS , Identity Authentication Service , BC-CP-CF-SEC-IAM , UAA, Authentication, Authorization, Trust Mgmnt , BPI-PA , SAP Build Process Automation , Problem