3. The method of claim 2 , wherein each similarity score compares similarity and diversity of the contents of the electronic message and contents of a respective one of the electronic messages of the associated cluster.
3. The method of claim 2 , wherein each similarity score compares similarity and diversity of the contents of the electronic message and contents of a respective one of the electronic messages of the associated cluster. 4. The method of claim 3 , wherein each similarity score is computed based on a comparison of (i) an intersection of respective features of the selected electronic message and a respective one of the electronic messages in the associated cluster and (ii) a union of respective features of the selected electronic message and a respective one of the electronic messages in the associated cluster.