Hillary Clinton's presidential campaign prohibits employees from using a personal email address to conduct official business, according to a hacked copy of its employee handbook.

"Staff are provided an e-mail account for Campaign business use only. Employees must use their Campaign-provided e-mail accounts for all correspondence regarding or related to the Campaign’s business," the handbook states.

"Employees cannot use personal email addresses (.gmail, icloud, etc.) to conduct Campaign business."

Like the campaign, Hillary Clinton's State Department also had rules governing the use of personal email addresses that Clinton was found to have violated.

An email containing the employee handbook was one of thousands released by the group Wikileaks after hackers believed to be acting in concert with the Russian government breached campaign chairman John Podesta's gmail account.

The email also contained the Clinton campaign's document retention policies, which instruct employees on the legal requirements for retaining internal records that could be subject to future legal action.

"Failure to retain documents subject to a litigation hold can result in the imposition of harsh fines and other penalties on HFA and, in some cases, on the individual," the document advised.

State also had strict records retention policies in place. Clinton's use of a private email server, which prevented her messages from entering the agency's custody in the first place, also ran afoul of those regulations.