Hi,
You will have to enhance extract structure BIW_KNA1_S for the field E-mail. This is done by creating an append structure with field E-mail and writing some coding to populate the new field.
The coding is usually done by implementing BAdI RSU5_SAPI_BADI or Enhancement RSAP0001. E.g. please refer to document How to Implement BAdI for Enhancing the Datasource in ECC.
Last but not least: if you are looking for a solid implementation framework, please have a look at my document Implementing Extraction Enhancement using SAPI BAdI - Encapsulation via Enhancement Spot.
Best regards,
Sander
