Hi Cbakumar,
I notice that you are on the site at the present time and Mister Macawber is away. So I hope the both of you don't mind if I jump in and try to assist.
1) Send you letter (incorrect)...I will send a letter or I will send you the letter (most--but not all--cases it is "a" letter)
2) send to you letter (incorrect...see above)
3) Write to you letter (incorrect) ....I will write you a letter. I will write to you.
4) Send the letter to you. (good) Or I will send a letter to you. Use "the" if it is a specific letter. If you are waiting for a business proposal, then you might be waiting for THE letter.
Or my friend usually writes to me every couple of weeks. I am waiting for a letter from her now.
A slightly correction to Mister Macawber's version. In the first paragraph of the letter there is the following sentence:
"Due to my laziness more than my work load, I didn't even congratulate you when I heard that you have passed your exams with 1st class and you have been promoted to the next rank."
Beginning a sentence with "due to" is usually not strictly correct. It is a pedantic point. I would rewrite the sentence as follows:
"Because of my laziness more than my work load, I didn't even congratulate you when I heard that you have passed your exams with 1st class and you have been promoted to the next rank."
In order to understand why "Because of" has been substituted for "Due to" please see the following thread:
Post:41464
Again, I didn't mean to intrude on your discussion. I just noted that cbakumar was at the site and Mister Macawber was away. So I thought I might be able to address his concerns while he is here.
Hope this helps.
MountainHiker