02 April 2014
in circular 04/2014, income tax department while extending due date for receipt of ITRV for AY 2009-10, 10-11 and 11-12, has suggested that it should be sent only via speed post.
however, notification on 21 March 2014, for extending due date for AY 2012-13 and 13-14, have given option for both speed post and normal post.
After that though there are news articles stating that department will only accept speed post, there is nothing on the official website of tax department to that effect.
So there is a dichotomy within department's instructions.
However, conservatively, you may use speed post only.