Yahoo's Zimbra Collaboration Suite (ZCS) and Google's Gmail are considered the two leading pretenders to the corporate e-mail throne held by Microsoft's Exchange. But a small Austin-based vendor is using Zimbra to complement, not replace, Microsoft's market-leading e-mail server.

MXToolBox on Wednesday introduced a new version of its e-mail continuity service for Exchange users that relies on Zimbra's mail server and Webmail client. Zimbra, which was acquired by Yahoo late last year, released a Version 5.0 upgrade of ZCS in February that lets end users synchronize e-mail, contacts, calendars and to-do lists with Microsoft's Outlook 2007 mail client.

The Zimbra-based offering from MXToolBox provides a backup option in case a company's Exchange servers fail or are knocked out of service because of natural disasters or other problems. MXToolBox is one of numerous companies offering Exchange backup services; many are hosting companies that provide replication and failover from on-premise Exchange servers to hosted ones.

Perhaps the best-known vendor is MessageOne, which was bought by Dell in February for US$155 million. But services such as MessageOne's tend to be much pricier than MXToolBox, which charges customers a monthly fee of $1.99 per user.

"MessageOne has a 'Cadillac and gold cufflinks' solution that is targeted at companies with 1,000 users and up," MXToolBox CEO Eric Rachal said. In contrast, MXToolBox, which Rachal founded in 2005, targets companies with 10 to 1,000 Exchange users. Rachal said that the company currently manages backup services for about 35,000 Exchange mailboxes at 1,000 or so organizations.

About one-third of MXToolBox's customers are located in hurricane-prone coastal areas in the southeastern U.S. For example, the New Orleans suburb of Slidell, La., was devastated by Hurricane Katrina in 2005. After the storm hit Slidell that August, it took 12 days to restore the municipal government's Exchange e-mail servers, said John Autry, Slidell's information systems manager.

Slidell added MXToolBox's backup service the following year, when incoming spam prevented city employees from sending e-mail messages and Autry found himself unable to switch the e-mail system to his backup Exchange hosting provider. The city hasn't had a crippling e-mail outage since then, according to Autry. "Our server is completely locked down," he said.

MXToolBbox uses Zimbra's software to make copies of all incoming e-mail on its own servers before passing them on to Slidell's Exchange servers. The vendor also uses Google's Postini antispam technology to filter messages sent to Slidell's 150 municipal workers.

For most of MXToolBox's customers, the risk to e-mail service comes less from Category 5 hurricanes than it does from incidents in which their Exchange servers fail to boot, Rachal said.

He claimed that in addition to offering users a Web-based mail backup to Exchange, ZCS provides a stealth introduction to the merits of fully hosted e-mail. Already, about 10 per cent of MXToolBox's clients have switched off Exchange completely in order to use the company as their primary e-mail provider, Rachal said.

Autry said he's "old school" and "likes to have more control," two reasons why he hasn't switched Slidell's primary e-mail system over to a hosted solution such as MXToolBox thus far.