ERMS:internal recipients missing in some sender

Hi Experts,

We have implemented ERMS solution in CRM 7.0 system.For some senders(Kind of SPAM) ,The internal recipients is always blank in SOIN transaction.On the other hand, if I filter all those who are not tagged with internal recipients in SOIN transaction, 99% are due to spam mails.

Pleasse provide me some inputs what may be the reason for not picking up the internal recipients. Is there any way we can turn off this since the number of spams captured is so little...

Thanks in advance.

Regards

Shanmuga