In charge of full service email deployment and strategic support, Epsilon has been appointed to target AOL's 2m customers.
Claire Pritchard, senior manager of data strategy at AOL Broadband, said: "We are delighted to have chosen Epsilon to provide the technology that manages our many customer relationships through personalised email communications and timely dialogue."
Epsilon will also be responsible for driving traffic to toy and game manufacturer Hasbro's website by managing its email delivery and creating email campaigns.
Helen Genia, online manager at Hasbro, said: "We chose Epsilon because of its demonstrable retail experience and notably its relationships with other blue chip retailers."
Children's charity NSPCC has also appointed Epsilon, which provides email programs for hundreds of companies, including Expedia and The Washington Post.
Ian Hitt, managing director of Epsilon International, said: "These three organisations are household names and each has recognised how Epsilon can deliver a measurable return on investment at a time when marketing budgets are under pressure.
"AOL Broadband and Hasbro see Epsilon's market-leading technology and, most importantly our investment and commitment to service, as critical qualities. We're delighted to have them on board and look forward to a long-term partnership."
Epsilon International clients also include Nectar, Electronic Arts, Ogilvy, Procter & Gamble and Tesco.