The Huffington Post, the US media outlet that received the latest series of emails, said they showed Yousef al-Otaiba denigrating Trump and others in communications with officials close to then President Barack Obama.
The Huffington Post said one of the emails showed Otaiba corresponding with Rob Malley, Obama's chief adviser on the Middle East, on election night.
"You got room for me in Abu Dhabi?" Malley wrote to Otaiba.
"This isn't funny," the UAE ambassador responded. "How/why is this happen. On what planet can Trump be a president."
In another exchange from 2016 with Judith Miller, a right-wing US commentator who reportedly sent Otaiba a series of tweets from a Saudi whistle-blower that criticised Emirati Crown Prince Mohammed bin Zayed Al Nahyan, the UAE diplomat said "the 7 minutes I spent reading this was the equivalent of watching 7 minutes of Donald Trump. A waste of my time."
The latest email leak comes after US media reported on Saturday that emails, released by a group called "GlobalLeaks" - not affiliated with the software developer, GlobaLeaks - showed clear collaboration between Otaiba and a pro-Israel think-tank in an attempt to discredit Qatar.
Otaiba is a well-known figure in US national security circles - he has been called "the most charming man in Washington" - and has participated in Pentagon strategy meetings at the invitation of defence officials.
Al Jazeera's Shihab Rattansi said those behind the leak told Huffington post that "their intention is to reveal the 'two-faced nature' of Emirati foreign policy".
He added that "from these emails it would appear that the ambassador to Washington doesn't have a very high opinion of Trump".
Huffington Post reporter Akbar Ahmed told Al Jazeera the emails "certainly shows a high level of UAE scepticism over Qatar".
Ahmed added that the emails also reveal that the "prime focus" of UAE officials in public "is Iran or the Muslim Brotherhood", but "it seems that a prime focus of these messages has been about neighbouring state Qatar".
He said this showed the UAE's "influence, their access and the kind of agenda they're pushing".
US and UAE officials have not commented on the recent leak.
On Monday, the UAE, along with Saudi Arabia, Bahrain, Egypt, Yemen and the Maldives cut off diplomatic ties with Qatar, a move Qatar's foreign ministry called "unjustified" and "based on claims and allegations that have no basis in fact".
The dispute between Qatar and the Gulf's Arab countries escalated after a recent hack of Qatar's state-run news agency. It has spiralled since.
Following the hack, comments falsely attributed to Qatar's emir, Sheikh Tamim bin Hamad Al Thani, were published.
Qatar's government categorically denied the comments.
"There are international laws governing such crimes, especially the cyberattack. [The hackers] will be prosecuted according to the law," Mohammed bin Abdulrahman Al Thani, Qatar's foreign minister, said on Wednesday.
UAE-based Sky News Arabia and Al Arabiya kept running the discredited story, despite the Qatari denials.
Source: Al Jazeera News