Hi chen,
This can be done in the .htm page by commenting the code which is responsible for this block.
Open component 'CRMCMP_CCS_EML’ . Now go to the ViewSet 'CRMCMP_CCS_EML/MailRightViewSet ' in the runtime repository you will find the view area named as 'MailInteractionArea '.
And now if you will see in the .htm page of view set 'MailRightViewSet.htm' there is a code
This is responsible for the Current Interaction record assignment block. Comment out the code highlighted above .
Thanks
Kumar.