Microsoft Corp. said it would release a public beta of Exchange Server 2010 on Wednesday, and said the final version of its flagship communications software would be released by year's end.Improvements to Exchange Server 2007's successor include a built-in e-mail archive and other features for e-mail administrators, as well as innovations aimed at end users that either match Google Inc.'s Gmail or, in some cases, top it. One thing that will not change: Exchange 2010 will continue to use the Jet database engine to store messages, instead of SQL Server as Microsoft publicly outlined earlier this decade. Jet has been criticized for not scaling well for companies with many e-mail users or large in-boxes. Julia White, director of Exchange product management, said that Microsoft had "done a ton of innovation" on Jet for Exchange 2010. "We're optimizing what we've done with Jet to move it to the next level." However, White was unsure if Jet would be used for later versions of Exchange.