you can send the CDF to retail.dox.india@citi.com via email. you can also send it via post:
Citibank N.A., Mail Room, ACROPOLIS, 9th Floor, New Door No.148(Old No.68), Dr Radhakrishnan Salai, Mylapore, Chennai - 600 004.
Citibank N.A., P.O. Box No. 4830, Anna Salai Post Office, Chennai - 600 002.