I was searching in google, but I could not find an explanation about that.
If I say: "You sent it to me", is that correct? Or do I have to say "You have sent it to me"?

I see both in several situations and I don't understand if it's correct gramatically.

For example, here: http://www.ourfuture.org/blog-entry/you-sent-message-fox-news
It says: "you sent".

Now look here: http://groups.google.tl/group/Gmail-Help-Logging-In-en/browse_thread/thread/f4cb044925a1991b
It says: "you have sent".

If I say: "You sent it to me", is that correct? Or do I have to say "You have sent it to me"?

Let me ask you to consider these two examples.
I cooked dinner. Describes a simple past event. Maybe I did this 30 minutes ago, or 30 years ago.
I have cooked dinner. This describes a past event that is important at the present time. It often means that dinner is on the table and it's time to sit down and eat.

Both of your examples are fine, but they are different tenses with different meanings. Use the search box to search the Forum for discussions about Present Perfect tense. You'll find many explanations. After you have done that, and if you are still unclear, please ask us again.

Best wishes, Clive
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Both are OK.

Sometimes they are interchangeable, but "you have sent" suggests that you sent it relatively recently, and that your sending it (and my receiving it) is relevant to the present situation. For example, you would not normally use "you have sent" for something was sent twenty years ago. It can also be used for emphasis ("You have sent it to me").

"You sent it to me" can be used for either recent or distant events.
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