First of all, thanks everybody for your answers.
Lucia, when I'm offline the IM's go to my email. So...
In the image below I attach, you can see the message that I get in my email. And now the big question: Which f... avatar does this ID correspond to? Well, the great answer: it's mine!!!. Therefore, it means when I am offline I send myself an email stack automatically. But when I'm connected, I don't get anything.
What do you think can cause these auto-send messages? I have removed all my objects that I had in my land to rule out that it's not due to some script of any object, but it hasn't been solved.