NEW YORK (CNN) -- The good news is that neither snow nor sleet is deterring U.S. postal carriers from their appointed rounds.

The bad news is, the delivery rate just rose. Postal rates increased Sunday for the first time in four years, raising the cost of a first-class stamp from 32 to 33 cents.

Overall, the increase across all classes of mail averages 2.9 percent, the lowest increase in postal service history, officials said.

The new 33 cent stamps have a Lunar New Year design depicting "The Year of the Hare," officials said.

The two pound rate rate for Priority Mail service increases 20 cents to $3.20.

Postcard rates remain unchanged at 20 cents, and international postal rates are also unaffected.

The rate increase will fund infrastructure, vehicle, and equipment improvements, according to a U.S. Postal Service spokesman.