While he said he looked into the classification issue, he dropped the matter upon learning it involved Benghazi.
In the mail, RNC Chief Counsel John R. Phillippe Jr. said the alleged attempt to make a backroom deal to cover up the extent to which US national security was put at risk is shocking and warrants an immediate review.
McCauley acknowledged, "it was a quid pro quo; I don't deny it".
FBI records said that Undersecretary of State Patrick Kennedy tried to convince the FBI that one e-mail on Clinton's private server should not be classified 'secret.' In return, one FBI official said, the State Department offered to help the FBI with its request to add agents in Iraq.
"This allegation is inaccurate and does not align with the facts", State Department spokesman Mark Toner said. "I need a favor, '" McCauley told the Post.
In that initial conversation, Mr. McCauley said, "it was a quid pro quo; I don't deny it".
The Monmouth University poll released on Monday put Clinton ahead of Trump, 50 per cent to 38 per cent, Politico news magazine reported. She has her own troubles and is certain to be asked about the latest revelations involving her use of a private email server during her time as secretary of state. "All I can say is that there was no quid pro quo".
McCauley had been trying to reach Kennedy about the issue of office space for agents in overseas embassies and consulates because he had a say in allocating space at diplomatic outposts. "I said, 'Absolutely not, I can't help you, ' and he took that, and it was fine".
The FBI maintained the email should remain classified.
Clinton had initially claimed that none of her emails contained classified information.
"We take very seriously our responsibility to decide whether our documents are classified or not classified". I need our people back in Baghdad.' " It was only then, said McCauley, that Kennedy explained what he wanted: the Federal Bureau of Investigation to mark a particular email that had traveled through Clinton's private email server as unclassified. "It's a matter of integrity".
[An] FBI official [in the worldwide operations division] spoke with Kennedy and Kennedy raised the possibility of keeping at least one Clinton email from public disclosure by obtaining a "B9" exemption under the Freedom of Information Act, a rarely used exemption that refers to "geological and geophysical information and data". I said: "Good, I need a favor".
For the FOIA requests related to the 30,000 CLINTON-related emails and the Congressional inquiry that requested Benghazi-related emails, those [sic] review process were handled outside the normal chain of people.
The agent, who kept anonymous and handled the security of Hillary Clinton in the period in which she was Secretary of State, made this statement in the investigation of server utilization private email by Democrats during the period that she led the U.S. diplomacy. "There was no quid pro quo even suggested or any kind of bargain laid on the table".
Ultimately, the FBI decided the email should be classified - a significant finding because the law enforcement agency had not yet launched its high-profile criminal investigation into the mishandling of classified information by Clinton and her aides.
The Republican is hoping to turn the conversation away from the allegations of sexual misconduct that partly dominated his last debate against Clinton.
The use of the phrase "quid pro quo" actually arises in a separate interview with a different FBI official from the bureau's records management division.