"Expert technical analysis showed the (COP28) office shared email servers with [Abu Dhabi National Oil Company] Adnoc," The Guardian newspaper reported.
It said it detected the link after it requested comment from the COP28 office in mid-May, without mentioning Adnoc, about criticism of Sultan al-Jaber, and received a reply marked "Adnoc classification: internal."
The newspaper said the COP28 organizers later acknowledged that it had consulted the oil company about the email.
The COP28 office had earlier claimed that it used separate computer servers from Adnoc, but the newspaper said "expert technical analysis" of the emails showed that the company had sent and received emails from the COP28 office.
The United Arab Emirates drew strong criticism for appointing al-Jaber to chair the U.N. summit, where delegates will discuss how to rein in deadly climate change, including the role of fossil fuel carbon emissions in driving global warming.
U.S. and E.U. lawmakers as well as campaigners have called on al-Jaber to step down from the role, citing a conflict of interest.
Al-Jaber's aides and the U.N.'s climate body, the United Nations Framework for Climate Change [NFCCC], did not immediately respond to requests for comment.