What does "do" mean here and why did "do" come before "you"? Shouldn't it be "not only you do send me pictures"?
"Do" functions as an auxiliary verb in this sentence. In this particular sentence, it means to achieve or complete something or to take part in an action. The reason it comes before "you" in this sentence is that it is the action that the person sending pictures takes part in. If you say "not only you do send me pictures" you will be using incorrect grammar. It also sounds very odd to a native English speaker. There are instances where "do" comes after "you" but it is dependent on the sentence and where the subject is placed in the sentence. Here are some examples of "do" being used with some sentences that have "do" after "you." Ex: You do such amazing work! Ex: I want you to do something. Ex: Will you do me a favor?