Hi Maren,
I believe you could have got this with some basic search in SCN.
Get the partners from CRM CRM_ORDER_READ and then use BUPA_ADDRESS_GET_DETAIL to get the email. Here you can get the email address in ET_ADSMTP.
@Srinivas: I don't think CRM_LOY_MSH_EMAIL_ADDRESS is suitable for this requirement as there is no membership or loyalty in picture. There is a good chance to fail the FM when there is no corresponding membership created for a BP if we use this FM.
Thanks,
Faisal