New York-based Return Path, which had a tense relationship with its left-coast competitor, said the deal will give it more scale in the "trusted e-mail delivery" market.
"While fiercely competing in the marketplace does create some degree of tension or even mistrust between two companies, that activity also creates a lot of common ground for discussion about the market and the future," Return Path CEO Matt Blumberg said in a statement on the company's Web site. "More scale is a good thing."
The 9-year-old Return Path develops e-mail technology that guards against spam and viruses. Habeas, its younger, 6-year-old rival, also provides ISPs with white-lists, or approved sender lists, to guard against junk mail. About three months ago, Habeas posted a note on its Web site saying that it was exploring its options for acquisition.
The deal is expected to close August 18. Return Path plans to maintain Habeas' Silicon Valley office and "most of its staff," according to the company.