As businesses become more reliance on information technology, electronic information is often produced as vital evidence during civil litigation. The process of discovering electronic information as evidence is getting increasingly expensive as the volume of data explodes. This surging demand calls for a solution to reduce the cost associated with the discovery process. In this paper, we propose filtering included emails as a means to reduce review data volume, and describe efficient algorithms to identify those emails. Experiments show that this can reduce the number of emails to be reviewed by 20% in corporate email corpse.