If you already did send, then "I have sent to you..." If you are going to send in the future " I will send you" or "I will send to you".

I understand that you want to know whether you use "to" or not. The correct way ("true" is not the right word here) depends on the structure of the whole phrase. "I send you a message" is correct. "I send a message to you" is also correct. "I send to you a message" is not correct (unless you wanted to sound very poetic).

Jonathan is right for past and future. If you're talking present tense, though, it is "I am sending you".