unknown@unknown Contact in eMail Response

Whenever an email is sent from an email id (customer email id) that doesn’t exists in Contact records in Siebel. eMail Response workflow starts fail and the SR or Activity records are not created.
Reason:
Siebel eMail response functionality works in such a way that takes the "from address" in email and query it in contact records. If the record is found then the wf proceeds, but if it is not found/ fails to get the contact record then it searches for an email address ‘unknown@unknown’ in the Contact records.
If a contact record exists with email id as ‘unknown@unknown’ then it moves on to create an Activity or Service request (whatever you have configured) with that contact and if it is not able to find the record, workflow fails to create an Service Request/Activity
Solution:
Create a contact record in Siebel with email id as unknown@unknown
Or
Modify the workflow to look for such unknown email address that already exists.