The signature on Calcutta High Court judge Soumitra Sen's resignation letter - which was faxed to President Pratibha Patil on Thursday - has been found "not original", the spokesperson for the president said.
"The signature in the faxed letter has been found not original. We are waiting for the hard copy of the letter to arrive and check the signature," Archana Datta, spokesperson of the president, said on Friday.
"Let the letter come. Any decision by the president will be only after that," she added.
Meanwhile, the president's office has handed over the faxed letter to the Department of Law and Justice, the spokesperson said.
Sen, against whom an impeachment motion was passed in the Rajya Sabha for financial irregularities, announced his resignation in Kolkata on Thursday through his lawyer.
The Lok Sabha was due to take up the impeachment proceedings Sep 5. Sen sent a copy of the letter to Lok Sabha Speaker Meira Kumar too.