automatic GL account posting.

hello gurus,

when we make purchase order and goods reciept for consumable and for external services,there is a need for entering account assinment,GL account manually entered by user

but my client wants that account assignment,GL account are automatically assigned by system,so pls tell me whether sap mm support this functionality? if yes pls let me know customization steps and neccesary detail for completing this scenario.

Thanks In Advance

Sumit Simran