"There is definitely a trend in the data center toward Linux" alternatives, Londini said. In addition to PostPath, vendors Scalix, a wholly owned subsidiary of Xandros, and Zimbra, which is owned by Yahoo, also offer Exchange replacement software that runs on Linux.

Michael Osterman, principal of Osterman Research, said all three vendors -- PostPath, Zimbra and Scalix, as well as others like Open-Xchange -- offer good Exchange alternatives for users.

With PostPath, the lack of any plug-ins can be a benefit, Osterman said, because it can simplify your deployment and system. But it's not the only thing to look for, he said.

"The thing with plug-ins is it's just another step," he said. "It's not a deal breaker probably for a lot of customers, because you can do automated installs remotely" to ease their installation and configuration. "But if you can get away without a plug-in ... then it's probably a better choice for administrators. It removes one layer of complication."

For users, Osterman said many more are willing to replace their backend e-mail infrastructure if they can leave their client software alone so users can continue to use what they know. That's why these Exchange alternatives are gaining in popularity, he said.

"We find that a dramatically larger percentage of companies would consider the new messaging systems if they didn't have to do anything to the desktop," he said. "If you consider the logistics of dealing with an upgrade like this, if you can go with PostPath [or one of its competitors] and just replace the backend ... then essentially to the users, there's no difference."