Sending money through a mail is not illegal if you are preferring cheque, bank drafts, postal orders etc. In case you want money transfer Via Currency notes then it is certainly illegal. In India Post has not implemented any technology to monitor its services on vigilance in all modes of transmission and with the limited offices under the CCTV cameras surveillance. So, there is always a high risk of getting stolen and even there is no definite procedure to trace out the person even there is a provision to inspection by respective Inspectors of posts. The better way of transfer money abroad is to go for the online money transfer.