Starboard Value earlier this morning announced a 13.3% ownership stake in Office Depot, making it the company's largest common shareholder. Starboard announced that it delivered a letter to the company's CEO, Neil Austrian, and its board of directors. In the letter, Starboard said it believes Office Depot is "deeply undervalued” and that it sees an opportunity to improve the company's performance and valuation. Starboard stated that Office Depot could meaningfully reduce its expenses, downside to smaller store formats, and that the retailer’s Office Depot de Mexico joint venture could be worth more than 50% of the company's entire enterprise value. News of Starboard Value's activist stake has Office Depot’s shares up 6.5%, or 16c, to $2.63 in early trading.