WASHINGTON — In a victory for unions, the National Labor Relations Board ruled Thursday that employees can use their company e-mail accounts for union organizing and other workplace-related purposes — if they do it on their own time. Once an employer gives an employee access to the company e-mail system, then the business cannot restrict what the employee e-mails, so long as it is generally workplace-related and isn’t during working hours, the NLRB ruled. The ruling said that “the use of e …