The emails were first reported by BuzzFeed and the Intercept after being posted under password protection on DCLeaks.com, a site with ties to other recent hacks of U.S. political figures and groups. A Powell spokeswoman confirmed to The Washington Post that the emails are Powell's.
"We have confirmed that the general has been hacked and that these are his emails," spokeswoman Peggy Cifrino said. "We have no other comment at this time."
The Washington Post has also accessed the emails. While they are still being combed through, here are the highlights of what we've seen:
On Trump and the 'racist' birthers
Of the birther movement, which Trump led earlier this decade by publicly questioning whether President Obama was born in the United States, Powell said its underpinnings were clear.
“Yup, the whole birther movement was racist,” Powell wrote to journalist and former aide Emily Miller on Aug. 21. "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 added: "As I have said before, ‘What if he was?’ Muslims are born as Americans every day."
Powell added in August 2015, according to the Intercept: Trump "appeals to the worst angels of the GOP nature and poor white folks."
What Donald Trump is doing on the campaign trail
Trump takes black people 'for idiots'
In another email to Miller on Aug. 21, Powell scoffs at Trump's apparent effort to reach out to African Americans in recent weeks and says Trump takes them "for idiots."
"He is at 1% black voters and will drop. He takes us for idiots," Powell writes. "He can never overcome what he tried to do to Obama with his search for the birth certificate hoping to force Obama out of the Presidency."
Blaming the media for the rise of Trump
"It is time to start ignoring him. You guys are playing his game, you are his oxygen," he wrote to CNN's Fareed Zakaria in December. "He outraged us again today with his comments on Paris no-go for police districts. I will watch and pick the timing, not respond to the latest outrage."
(So-called "no-go" zones are places in Europe allegedly so dominated by Muslims that police have given up trying to monitor them. There is little evidence that they actually exist.)
Powell suggested in another email that even critical coverage of Trump didn't really work: "To go on and call him an idiot just emboldens him."
Trump 'has no sense of shame,' is 'a disaster'
Writing in July 2015 after Trump publicly aired the phone number of Sen. Lindsey O. Graham (S.C.), a onetime rival GOP presidential candidate, Powell said: “Trump has no sense of shame.”
In addition to calling Trump, "a national disgrace and an international pariah," he also calls him a "disaster" on July 24.
Fuming about being tied to Clinton's emails
Powell's rancor is not reserved solely for Trump. And Clinton's decision to cite his use of private email as secretary of state to justify her private email server has clearly proven a sore spot -- both in these emails and in previous Powell comments.
"I have told Hilleary's [sic] minions repeatedly that they are making a mistake trying to drag me in, yet they still try," he wrote in May to former top Bill Clinton adviser Vernon Jordan. "The media isn't fooled and she is getting crucified. The differences are profound and they know it."
The two situations aren't completely analogous, as The Post's Fact Checker has written, but Clinton has used Powell to suggest that her private email server was not totally novel.
Just last month, Powell suggested that Clinton had shot herself in the foot by not apologizing immediately and by dragging out the email story. “HRC could have killed this two years ago by merely telling everyone honestly what she had done and not tie me to it," he said, according to the Intercept.
Hillary Clinton’s campaign comes to an end
'Everything [Clinton] touches she kind of screws up with hubris'
In August 2015, Powell said to Democratic donor Jeffrey Leeds that Clinton's email problems show how liable she is to create problems for herself — and to cause problems for others' use of official email.
"They are going to dick up the legitimate and necessary use of emails with friggin' record rules," he wrote. "I saw email more like a telephone than a cable machine. ... Everything HRC touches she kind of screws up with hubris.”
Clinton comes across as sleazy 'for good reason'
On Aug. 1, after Andre Lewis asks Powell about when Powell might want to endorse Clinton in the presidential contest, Powell seems to be hesitant to jump on-board with her.
"Hillary has not been covering here [sic] self with glory," Powell writes. "For good reason she comes across as sleazy."
Whether Powell endorses or not, it seems clear he won't be overjoyed about it. On July 26, 2014, Powell emails Leeds and says he would "rather not have to vote for" Clinton, "although she is a friend I respect."
He then cites tabloid reports about Bill Clinton continuing to have affairs with "bimbos."
Saying Clinton doesn't look well
Count Powell among those with early questions about Clinton's health.
Powell chatted with Leeds in March 2015 about a column from conservative writer Peggy Noonan titled "Hillary Seems Tired, Not Hungry." Powell suggested Noonan was on the right track.
"I think there is something to it. On HD tv she doesn't look good. She is working herself to death," Powell said, adding: "She will turn 70 her first year in office."
Leeds then recounted something Sen. Sheldon Whitehouse (D-R.I.) told him about a joint event at which, according to Leeds's recounting of Whitehouse's comments, Clinton "could barely climb the podium steps."
Calling Benghazi a 'stupid witch hunt'
One area in which Powell has sympathy for Clinton is on Benghazi, the GOP reaction to which he labeled a "stupid witch hunt," as BuzzFeed first reported. And fellow former secretary of state Condoleezza Rice appeared to agree.
"Benghazi is a stupid witch hunt. Basic fault falls on a courageous ambassador who thoughts [sic] Libyans now love me and I am ok in this very vulnerable place,” Powell wrote to Rice in December 2015, referring to former ambassador to Libya J. Christopher Stevens, who was killed in the attack.
Powell added, though, that Clinton bore some blame: “But blame also rests on his leaders and supports back here. Pat Kennedy, Intel community, [State Department] and yes HRC," referring to Clinton.
“Completely agree,” Rice responded.
Correction: This post initially attributed a comment that "no one likes" Clinton to Powell, but it was written by Leeds in an email to Powell. The references have been removed.