He also called the birther movement, which the Republican presidential nominee helped lead, "racist."
"That's what the 99% believe. When Trump couldn't keep that up he said he also wanted to see if the certificate noted that he was a Muslim," Powell wrote in an August email.
The messages, the existence of which were first reported by BuzzFeed
and The Intercept
, were posted to DCleaks, an organization affiliated with other recent hacks of high-profile figures.
Peggy Cifrino, an aide to Powell, told CNN: "The emails are accurate. No further comment at this time."
The emails are notable for their candor about Trump. Powell, who oversaw the State Department during the beginning of George W. Bush's administration, hasn't endorsed Trump and has largely sidestepped questions about his thoughts on the controversial GOP nominee.
Powell also lampooned Trump's proposal that he could win over the African-American population.
"For him to say yesterday that within four years he would have 95% of blacks voting for him is schizo fantasy," Powell wrote, adding, "And (former Fox News chief Roger) Ailes as an adviser won't heal with women."
Moreover, the former secretary of state tore into Trump as an embarrassing figure to represent the United States.
"Trump is a national disgrace and an international pariah," Powell wrote in June.
"He appeals to the worst angels of the GOP nature and poor white folks," Powell wrote in another email.
As Trump's lead in the Republican primary solidified, Powell complained to CNN's Fareed Zakaria about the network's political coverage.
"You guys are playing his game, you are his oxygen," Powell wrote in December.
On Wednesday night, Trump tweeted his disdain for Powell.
"I was never a fan of Colin Powell after his weak understanding of weapons of mass destruction in Iraq = disaster. We can do much better!" Trump said.
Clinton 'kind of screws up with hubris'
But the messages also showed Powell angry with Hillary Clinton over her handling of her personal emails as secretary of state.
As The Intercept reported
, Powell wrote in 2015, "Everything HRC touches she kind of screws up with hubris."
The FBI released information from its investigation of Clinton's email practices in July and August, and the notes it released showed Clinton indicating her practices came from Powell.
Powell pushed back against this publicly, telling People magazine in August that Clinton's people were trying to pin it on him.
He said as much in his email, writing on August 23: "(Clinton) didn't need any advice or ok from me; she was already doing it. I gave her written guidance on why and how I had been doing it."
Clinton appeared on CNN
shortly thereafter and told Anderson Cooper that the blame rested with her.
Cheryl Mills, a former staffer for Clinton, forwarded the transcript of Clinton's CNN interview to Powell, a leaked message shows.
He responded to Mills, calling the comments "very nice."
"The only thing I would add is to simply say she had a private account on a public server before becoming SecState and continued to use it when she became SecState. On the other hand this might to lead to questions about the basement," Powell said.
On August 28, he said that Clinton "could have killed this two years ago by merely telling everyone honestly what she had done and not tie me into it. I told her staff three times not to try that gambit."
Wednesday's email leak was not the first time Powell's private thoughts were revealed. In 2013, a hacker known as "Guccifer" infiltrated Powell's email. The Romanian hacker, Marcel Lazar, also managed his way into the digital spaces of some members of the Bush family and Clinton confidant Sidney Blumenthal.
Lazar was sentenced to 52 months in prison on September 1.
These leaks came from DCleaks on the same day a hacker by the alias "Guccifer 2.0" released more information
from the Democratic National Committee. Experts have pointed to Russian state elements as the actors behind the DNC leaks.
Powell, Rice talk Iraq War
An exchange in 2015 showed Powell and his successor, former secretary of state Condoleezza Rice, critiquing some of their former colleagues in the Bush administration.
Rice forwarded a link to story about Bob Woodward
slamming former Defense Secretary Donald Rumsfeld's recent commentary on the Iraq War.
Rice praised Woodward and added: "First, we didn't invade Iraq to bring democracy --- but once we overthrew Saddam (Hussein), we had a view of what should follow. If Don and the Pentagon had done their job ... things might have turned out differently."
Powell criticized "Doug and Paul," presumably Douglas J. Feith and Paul Wolfowitz, for their plan on Iraq and praised his former boss, President George W. Bush.
"43 (Bush, the 43rd president) knew what had to be done," Powell wrote to Rice. "As you say, the boys in the band were brain dead."