Good luck with further movement of the letter.
You should be able to track your letter (at-least until it reaches destination country) on India Post Website
. (This website works most of the times, but I can't give any guarantee for obvious reasons
) Once it has reached the destination country, it should be traceable on tracking website maintained by their postal authority.
Depending on which country you have sent the letter to, the custom's clearance can take any time between one to fifteen days (or in some cases, even more).