Hi,
you can try to search for documents with specific partner functions filled in - like 0000080* (eg. 00000804 is a receiver, 00000807 is a sender) - check table CRMD_PARTNER.
you can also try to look within SOFM objects searching with recipient , but this would be more difficult.
If you have TREX you could look using its search typing in email address. Search with TREX by ABAP is also possible - you can use BOL query for that.
BR
Radek