Paul N. Carlin, a Postal Service veteran who unsuccessfully challenged his firing as postmaster general for what he said was retribution by a corrupt board member but rebounded by starting two lucrative businesses that focused on rapid sorting of mass mail, died April 25 at a hospital in Arlington. He was 86.

The cause was bronchitis and pneumonia, said his wife, Azucena Carlin.

Mr. Carlin, an expert in business administration, became President Richard M. Nixon’s liaison with Congress on postal matters in 1969 and was a key player in the old Post Office Department’s shift in 1971 from a federal agency to the semiautonomous U.S. Postal Service.

He later became administrator in charge of the service’s largest region, based in Chicago, before being named postmaster general in January 1985. A year later, he was fired. A “changing environment that required a different marketplace perspective” was the official reason given for Mr. Carlin’s dismissal.

He contended that he had been forced out because he stood in the way of a kickback conspiracy involving the vice chairman of the Postal Service’s board of governors, Peter E. Voss. After an investigation, Voss pleaded guilty to criminal charges and was sentenced to four years in prison.

Mr. Carlin sued in federal court to get his job back. The case went to the Supreme Court, which in 1988 declined to review a lower-court ruling that the courts lacked power to intervene.

In his appeal, Mr. Carlin said: “If ever a case cried out for judicial review to protect individual rights, this is that case . . . . A postmaster general was removed from office by a vote which was fraudulently procured by a corrupt postal governor.”

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With partners, Mr. Carlin later went into businesses involved in mass mailings. In 2001, the United Parcel Service purchased his company Mail2000 for an estimated $100 million.

“Even the old gray-hairs can do it in a world with all these young fellas who were starting companies,” Mr. Carlin told the Washington Business Journal that year. “All we’ve done is taken technology and applied it to existing processes.”

Paul Nestor Carlin was born in San Diego on Aug. 25, 1931. He graduated from the University of Wyoming in 1954, then served in the Army for two years. He later studied advanced management at Harvard Business School.

Before joining the Postal Service, he worked in Washington as a specialist in federal relations for the National Association of Counties, the National School Boards Association and the National Audio-Visual Association.

Survivors include his wife of 63 years, Azucena Rodriguez Carlin of McLean; four sons, Joseph Carlin of Carey, N.C., Robert Carlin of Taiwan, Thomas Carlin of Salisbury, Md., and Mark Carlin of Dallas; two grandchildren; and three great-grandchildren.