Where can I expect to receive responses to applications for jobs in math departments at universities?
Based on my job search experience from a couple of years ago, there are three kinds of communications you might get by snail mail:


Equal-opportunity questionnaires, asking your race, gender, etc, for statistical purposes (usually not shared with the search committee).  Responding to these is optional, and certainly not time-critical.
Rejection letters.  Obviously these don't need any response at all, and they usually don't tell you anything you didn't already know; often they aren't sent until long after the search was obviously finished.
Formal offer letters. You'll know when these are coming, because you'll already have been informally offered the job by phone or email.  (And in some cases, you might have also had to negotiate what the offer letter will contain, though for postdocs it's more likely to be "this is our offer, take it or leave it".)  At that stage, you could ask the employer to be sure to send the letter to your home address.


All communications that are actually relevant to whether you get hired or not will take place by email, phone, Skype, or in-person interview.  Time is of the essence in hiring, and nobody wants the delay of snail mail for something that needs a quick response.