I have read on this site the discussion about when to use Present Perfect versus when to use Simple Past.
The cases explained are all clear and seem unproblematic to me, but what about the following:
A: Peter, have you answered David's mail?
B: Yes, I have answered that mail already yesterday / Yes, I answered that mail already yesterday.
The problem here is: on one hand, there is a TIME CLUE indicating the past ("yesterday" => Simple Past?), but the fact that the mail has been answered is STILL RELEVANT at the time of speaking, which suggests that Present Perfect should be used.
Further: I HAVE (?) learned in school (many years ago, but that is still relevant!) that "already" is often an indicator of Present Perfect. On the other hand, I have learned that you don't use Present Perfect when the event is (has been?) finished in the past and a time (indicating that this (has?) happened in the past) is given, or the word "ago" is used.
So which is correct?