WASHINGTON — The Postal Service Friday reported a $5.1 billion loss for the just-completed 2015 fiscal cycle — but that’s a slight improvement over last year.

The loss reflects continued erosion in the delivery of first-class mail as well as expensive mandates for upfront funding of its retiree health care obligations.

There was good and bad news in the Postal Service’s year-end results. Revenues were up, and it made an operating profit of $1.2 billion, reflecting continued growth in its package-delivery business.

But a special rate surcharge is set to expire next year, which promises to cut revenues by $2 billion annually, and volume of mail delivery should continue to shrink. Expenses continue to rise despite slower mail delivery.

The service is still seeking relief from the mandate to “pre-fund” retiree health benefits. Legislation in 2006 required the Postal Service to fund 75 years’ worth of retiree health benefits, something that neither the government nor private companies are required to do.