Add email_address to gift CSV

For GiveCampus reporting.

Add the standard payer_email column to the gift report in Reporting Settings/custom report columns. If the receiving system requires a header named email_address, use the report-column alias configuration for payer_email rather than adding an empty custom question/blank column with that name. Export a sample to verify both values and header; donor payer email is distinct from other contact/email fields.