Dell, the computer maker, said on Tuesday that it would buy the business e-mail services provider MessageOne, which was co-founded by Michael S. Dell’s brother, in an effort to compete with similar services provided by Microsoft and Google.

The $155 million cash deal is Dell’s latest in a wave of acquisitions ranging from small shops like the software company Everdream to the $1.4 billion purchase in November of the network storage provider EqualLogic.

MessageOne’s software, which is delivered to customers over the Internet, helps companies manage and archive e-mail messages, minimize failure and prevent data losses, Dell said in a statement.

Dell’s chief information officer, Stephen F. Schuckenbrock, said the acquisition would help the company compete against offerings “that are emerging in the market from companies like Google, like Microsoft and others.”

Last year, Google paid $625 million to acquire the e-mail security company Postini to bolster its online Apps service to make it more useful inside businesses.

Dell said MessageOne was partly owned by two investment funds: Impact Venture Partners and the Impact Entrepreneurs Fund. The founder and chief executive of Dell, Michael, and his family are investors in the funds, which are managed by his brother, Adam.

Dell said it expected Michael; his wife, Susan; and their children’s trust to receive about $12 million from the deal. Adam Dell will get about $970,000, and his parents will receive about $450,000.

Michael Dell intends to donate the proceeds to charity, the company said, adding that he was excluded from negotiating the acquisition.

Dell has stepped up the pace of acquisitions since Mr. Dell resumed the helm a year ago. Last month, the company completed the purchase of EqualLogic, its largest acquisition since the company was founded in 1984. EqualLogic specializes in data storage technology, Dell’s fastest-growing business.

Shares of Dell fell 22 cents, to $19.71.