U.S. Postal Service's (USPS) primary air cargo provider

as rival FedEx announced an end to its

more than 20-year partnership with USPS

USPS was the largest customer

for FedEx's air-based Express segment

even as payments declined after the postal service shifted

from planes to trucks as part of an operational revamp

USPS represented just about 4% of Express'

annual revenue, according to a Reuters calculation

The contract win is seen as a boost to UPS, which in

January forecast full-year revenue below Wall Street's target

The contract's financial terms were

not disclosed but UPS said it was 'significant'