I'm in the process of asking various faculty members to be references as I apply for jobs (both postdocs and industry jobs). So far, I've basically just been asking people are willing to be references in general. Many jobs just require that I give contact information for references. My first question is: do I need to ask/inform my potential references ahead of time about each job I apply to so they know who they may be getting a call from? Or do I need to tell them at least what types of positions I'm applying to (e.g., industry research scientist, academic postoc, etc.)? Or is it enough just to get their assent to list them as a reference?
Secondly, for reference letters, it seems most employers want me to have them send a reference letter directly. Are these letters supposed to be highly specific to the position I'm applying to? Part of why I ask is that, inasmuch as they are, I would be somewhat hesitant about applying to lots of positions, as it would be rather burdensome for my reference letter writers. Or, if the letters are fairly general, should I just give my letter writers a list of email addresses (and some information about associated positions)?