By default, the Email Address field on Project record is manually entered. See SuiteAnswers article Creating a Basic Project Record, Answer Id: 9321. This is for the reason that most of the Email Addresses on the Customer record is the Company's generic Email Address. E.g. firstname.lastname@example.org. This is to ensure that any email communication for this Project is sent and received by the recipient. Users may create a custom entity field that sources and automatically populates the assigned customer's Email Address.
1. Navigate to Customization > Lists, Records, & Fields > Entity Fields > New.
2. Enter a value for the Label field. E.g. Customer Email
3. Set Type to Email Address.
4. Unmark the Store Value checkbox.
5. Under the Applies To tab, mark the Project checkbox.
6. Under the Display tab > set Subtab to Main.
7. Under Sourcing & Filtering, set Parent for the Source List field and E-mail for the Source From field.
8. Click Save.