Yahoo (NASDAQ:YHOO) has announced plans to buy Zimbra, Inc., a next generation e-mail and collaboration software provider for a proposed $350 million. The acquisition would enable Yahoo to target the small and midsize business market.

Zimbra's e-mail service would allow small and midsize companies to host e-mail on or off premises with their own domain. Zimbra offers rich, AJAX-based email, calendar and contact management features, as well as creative mash-ups called Zimlets that tie in Web value to e-mail. Zimbra's open platform allows features to be customized to each customer's needs.

The acquisition is expected to be completed in the fourth quarter of this year.