Kendall was appointed U.S Postmaster General on May 1, 1835. During his time in office, he worked to eliminate corruption in the Post Office Department. He also manipulated operations of the Post Office Department so that western newspapers (which tended to support Jackson) were delivered faster and received better service than eastern ones. Despite having no legal basis for his action, he also allowed postal officials in the Deep South to refuse to deliver abolitionist literature. Suffering from extreme poor health, he resigned as Postmaster General effective May 18, 1840. John Quincy Adams, a bitter foe of both Jackson and Van Buren, confided to his diary in December 1840 that he believed both men had been "for twelve years the tool of Amos Kendall, the ruling mind of their dominion." Kendall wrote extensively for the "Washington Extra Globe" newspaper in the summer and fall of 1840 in an unsuccessful effort to boost Van Buren's chances for re-election.