This question is mostly aimed at mathematicians, since I am currently in the job market for tenure-track positions in pure mathematics.
Usually most of the job adverts say "three letters of recommendation" or "four letters of recommendation, one of which should address teaching", or variants of that. My concerns are:
1) is it ok to submit more than the number requested? Let's say they ask for 3 research letters; is it ok to submit 4? 2) same question for teaching letters: usually only one is required for research positions. I have two available at my disposal, since I had two employers that wrote me one. Should I submit both, or just the one that I think will be more beneficial?