Dear Vikash,
The service rendered by the vendor is under contractual basis. It is not a professional service. A profession or vocation is that where the qualified person only can do the job. On other person can fulfill his job as a substitute. The service about the mail box is not a professional service. Any employee of Rediff can provide you that service, provided you contract with them.
Therefore, Your vendor's contention is right. The situation falls under section 194C and not u/s 194J.
Secondly, regarding service tax,
Service tax charged has nothing to do with the TDS provisions. The TDS is to be made on the gross amount only. The only exception is Sec.194I where TDS is deducted on rents. Here, TDS is to be deducted on the net amount i.e. after deducting service tax. In all other cases except 194I, TDS is made on gross amounts.
Regards,
Bhagirath KS
<<corrections, suggestions welcome>>