Is recall more important than precision for mass mailings?
Neither.  What you really need is for the probability estimate to be accurate.  It's not enough to optimize just one of them (and you can't optimize for two metrics simultaneously, since better precision tends to lead to worse recall, and vice versa).

I suggest you minimize the cross-entropy loss function.  This is designed to help produce accurate estimates of the probability.  In some sense, that will optimize both precision and recall and trade them off in a particular way.  The specifics will depend on what classifier you use.