Unable to find customer mails in CRM mail inbox search.

hello experts

We are facing strange issue

customer sends mail to generic customer care mail ID , and is received/mapped to receive in SAP CRM  mail box search, and all mails will receive to outlook

but issue is that there are few mails sent from customer are received in out look but not there in CRM

as known if E-mail has more than 10MB it wont recieve in CRM

but said cases are less than 10 MB but sill we are not recieving in CRM

kindly assist

Regards

Chinna babu