Microsoft said on Tuesday it plans to offer a new standalone message transfer agent that runs on the edge of corporate networks to securely handle the flow of e-mail to and from the Internet.

Exchange Edge Services, which is slated to go into beta testing later this year and ship early next year, is a replacement for the current Simple Mail Transfer Protocol service that is part of Exchange. Microsoft made the announcement at the annual RSA Security Conference in San Francisco.

Microsoft is developing the standalone message transfer agent (MTA) to replace the current one in Exchange because that one has a dependency on Microsoft’s Internet Information Server and Active Directory.

That configuration can force administrators to leave ports open on the edge of their networks that can lead to security risks. The result is that few Exchange administrators use the current Microsoft MTA, opting instead for software from companies like Sendmail or a dedicated appliance offered by vendors such as IronPort.

“Edge Services will open the option for running the MTA at the edge [of the network],” says Dave Hebert, senior product planner for Edge Services at Microsoft.

But co-opting the MTA market is not Microsoft’s ultimate goal. The big picture is that Edge Services will become a sort of hub for plugging in third-party security services for protecting e-mail communication. Microsoft is rewriting the MTA in C# managed code under the .Net Framework and adding an API that will support third-party plug-ins. The MTA also will fall under the common management platform Microsoft is developing under its Dynamic Systems Initiative.

Microsoft partners Brightmail, GFI Software, Network Associates, Panda Software, Sybari Software, Symantec and Trend Micro said they plan to develop products for Edge Services.

Observers say many users will be reluctant to run the MTA on the edge initially but could use it internally.

“Folks will be careful with it and maybe put in on bridgehead servers or use it for internal routing,” says Matt Cain, an analyst with the Meta Group. “They will have to get comfortable with it before they put it on the edge.” But Cain said the future of the MTA as sort of a security hub is headed in the right direction. “It will be good to get third-parties to write to it and get hygiene services under the Microsoft security framework.”