1. A system for automatic generation of subject lines for electronic mail (email), comprising: an extraction module capable of extracting topics from an email message; a prioritization module capable of computing a sender relevance score for each topic, and ranking the topics based on the sender relevance scores; a sorting module capable of ranking a plurality of syntactic units from the email message based on the topic ranking; and an assignment module capable of assigning one or more subject lines to the email message based on the ranking of the syntactic units.