For earlier years, paper returns could be submitted except for Companies. For the companies, filing of e-return is mandatory from A.Y. 2006-07 onwards. For non-corporate assessee covered by audit u/s 44AB, filing of e-return is mandatory from A.Y. 2011-12 onwards.
ITR Form, Previous Year return filing The article explaines that the return filing for the companies is mandatory from AY 2007-08 onwards and returns of earlier years can be submitted manually.