Microsoft's Exchange Server may be the king of corporate e-mail, but it has plenty of haters, especially among smaller companies that find managing the software and dealing with e-mail backups to be a huge hassle.

Meanwhile, Microsoft's Outlook e-mail client has its issues -- sluggish performance, a user interface that isn't especially user-friendly and ever-increasing complexity. But it maintains a devoted following among the tens of millions of business workers who practically live in the software while on the job.

Not surprisingly, there is no shortage of alternatives that let you get rid of Exchange Server in your data center while keeping Outlook on the front end. They range from open-source Exchange clones to Web-hosted Exchange offerings from Microsoft and countless other service providers.

"If you're able to replace the back-end mail servers so no end users notice, then IT gets a less expensive e-mail infrastructure but doesn't have to deal with angry users set in their ways," said Guy Creese, an analyst at Burton Group.

Google's Gmail service joined the list of alternatives last fall, after Google added support for the Internet Message Access Protocol. IMAP enables rapid synchronization of messages between Gmail and desktop e-mail clients such as Outlook, and between the mail server and various end-user devices. And Gmail is free for some users and inexpensive for others -- a one-year subscription to Google Apps, which includes enterprise support for Gmail, costs US$50 per user.

"Many of my customers with under 50 employees don't even need Exchange, so I see a lot of growth in Outlook-to-Gmail," said Ronnie Mansoor, CEO of Implicit, a developer of Outlook add-on software.

However, Google didn't go all the way with its IMAP support: Users still can't download their Gmail contact lists or calendars into their Outlook e-mail clients.

Now a software vendor named Cemaphore Systems is publicly releasing a beta version of a tool that lets users synchronize their e-mail, contacts and calendars between Outlook and Gmail. That could make it possible for companies to use Gmail as an inexpensive disaster recovery backup to Exchange Server, or perhaps to dump Exchange altogether.

Cemaphore is taking signups from users who want to test its new MailShadow for Google Apps software, known informally as MailShadowG. The company said that a commercial release is expected to ship during the third quarter and will cost US$49.95 per user annually, although beta participants will be able to get the first year for US$29.95 per seat.

Unveiled several months ago, MailShadowG has already gotten some early-adopter praise. In March, blogger Robert Scoble raved that during a demo by Cemaphore, MailShadowG synchronized his e-mail and calendar between Outlook and Gmail in a matter of seconds. "Google's synchronizer sucks compared to Cemaphore's," he wrote. "It's slow and buggy."

"Google may sync every 30 or 60 minutes. We're firing as the events fire," Cemaphore CEO Tyrone Pike said in an interview on Tuesday. "That's why we call ours a continuity product, not a sync product."

Pike also claimed that MailShadowG doesn't create multiple versions of the same calendar event, a problem with some calendar synchronization software. "Our algorithm is very immune to that," he said.