Ensuring that users receive email notifications in ServiceNow requires verifying specific attributes on the user record:

A. The Email field must have a valid value: This is correct. The Email field should contain a valid email address, as notifications are sent to the address specified in this field.

B. The user must not be locked out: While it's important for user access, being locked out does not directly impact the sending of email notifications.

C. The First name and Last name fields must have values: These fields are for identification purposes and do not affect email notification delivery.

D. Active must be true: This is correct. Only active users are eligible to receive email notifications. If a user is marked as inactive, notifications will not be sent to them.

E. Delegation must be enabled: Delegation pertains to assigning responsibilities to another user and does not influence the receipt of email notifications.

For effective email notification delivery, always ensure that the user's Email field contains a valid address and that the Active field is set to true.