Secretary of State Rex Tillerson Rex Wayne TillersonGary Cohn: 'I haven't made up my mind' on vote for president in November Kushner says 'Alice in Wonderland' describes Trump presidency: Woodward book Conspicuous by their absence from the Republican Convention MORE used an alias email account during his tenure as CEO of Exxon Mobil Corp. to increase efficiency, attorneys for the company argued Thursday, saying there was nothing improper about the move.

"Mr. Tillerson’s use of the Wayne Tracker account was entirely proper," attorneys at the New York-based law firm Paul Weiss Rifkind Wharton & Garrison LLP wrote in a letter to a state supreme court justice. "Wayne Tracker" refers to the name used by Tillerson on the email account.

"It allowed a limited group of senior executives to send time-sensitive messages to Mr. Tillerson that received priority over the normal daily traffic that crossed the desk of a busy CEO," they added. "The purpose was efficiency, not secrecy."

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The company said that “technological processes” used to preserve internal emails for the probe “did not automatically extend to the secondary email account” and that it was working to determine whether that affected the preservation of the account’s emails.

In their letter, Exxon Mobile’s lawyers predicted that impact “will not be significant” for three reasons: the company had previously searched the account for relevant emails, many of the messages in the Wayne Tracker inbox would also be in Tillerson’s primary account and many of the senior executives who emailed Tillerson through the Tracker account were already part of the subpoena process.

New York Attorney General Eric Schneiderman's office on Monday alleged that Tillerson had used the account between 2008 and 2015 to discuss climate change. Schneiderman's office is investigating Exxon Mobile's knowledge of climate change and whether the company misled the public about its findings.

Officials subpoenaed Exxon Mobil for internal documents — including Tillerson's emails — regarding the investigation but argued that the Wayne Tracker emails were not turned over.

The attorney general’s office raised the question of the Wayne Tracker alias emails ahead of its filing last week, according to a source familiar with the case.

Exxon Mobil has already provided 2.5 million pages of documents related to the investigation, though only 160 of the documents are emails from the company’s management. The state attorney general's letter requested that the judge order the company to say whether the Wayne Tracker emails were preserved.

"More than 16 months after receiving our subpoena, Exxon is just now admitting it may not have preserved or produced the emails of its former CEO, who used an alias email account,” Amy Spitalnick, the press secretary for Schneiderman’s office, said in an email.

“We look forward to addressing these, and the other issues our letter raised, in court," she added.

Devin Henry contributed.

Updated at 10:38 a.m. on March 17.