E-mail marketing firm StrongMail Systems said Tuesday it had purchased social media marketing firm PopularMedia. Financial details were not disclosed, although both companies share Sequoia Capital and DAG Ventures as investors. PopularMedia has raised more than $12 million, including $8 million in a round last summer. One of the company’s products adds a “social layer” to standard banner ads in order to extend their reach; another is a widget that makes it easy for visitors to a website to comment about the content or share it on a social network. StrongMail, meanwhile, sells e-mail marketing tools. StrongMail said it would now be able to offer integrated e-mail and social media campaigns. Release.