Is the following grammatical?
Should I send the letter to her?
If it is, then how come that send can also be used without to?
Should I send her the letter?
What about the use of send in a sentence like "It sent her mad"?
In some languages, the noun denoting the 'recipient' of something is frequently in the dative case.
In English, the 'recipient' can be shown in two ways:
As an indirect object, usually preceding the direct object: He sent/gave me the letter;
Following the preposition 'to' following the direct object: He sent/gave the letter to me.
Some pronoun/pronoun and pronoun nouns are less commonly used than others.
I gave John the letter. I gave the letter to John.
I gave him the letter. I gave the letter to him.
I gave it to John.
I gave it to him.
I gave John it.
I gave him it.