Is it permissible to open a savings account at a post office that deals in usury, out of necessity?

It is not permissible to deposit money in usurious banks and institutions, whether with interest or without; because it involves cooperation in sin and aggression. However, if there is fear of its loss and no place to keep it, then it is permissible to deposit it without interest out of necessity, in order to commit the lesser of two prohibitions.