Nonprofit mailers are expected to save more than $1 billion in postage next year under a rate relief bill signed into law last month by President Clinton. The Nonprofit Rate Relief Act caps the U.S. Postal Service’s Standard A (advertising) Mail rates for nonprofits at 60% of its commercial rates and at 95% of its first class, periodicals and Standard B Mail rates. The caps are scheduled to go into effect Jan. 7, the same day the USPS hopes to begin raising $3.7 billion in new revenue with an across-the-board rate hike that averages 6.4%.