- I have sent this e-mail to Aman also.
- I have sent this e-mail to Aman too.
Which one is correct? What is the exact difference between the two? Please explain.
In the context you are asking about, the two words are very synonymous, so there is no "exact difference" between the two.
When I am choosing one over the other, my choice is often based on style, and how they sound. For example, in this sentence, I would use also, simply because it sounds better (who wants to say "two-too"?):
When I asked if they wanted a slice of bread, Jim asked for two, and Jane asked for two, too.
When I asked if they wanted a slice of bread, Jim asked for two, and Jane asked for two, also.
Moreover, this is a generality, but I think also usually sounds better in technical writing; it seems slightly more formal:
The graph shows that the function f(x) is continuous, and g(x) is continuous, also.
At the beginning of a sentence, also just about always the better word:
Also, I sent this email to Aman yesterday.
However, at the end of a sentence, when you're indicating "as well", there's really not much difference in which one you use (although a comma is generally used before too in this context):
I have sent this e-mail to Aman also.
I have sent this e-mail to Aman, too.
When used like you have here to mean as well, or in addition to, they are interchangeable.