Having already ascertained that there are a few issues with OS X Mavericks, with Mail being the biggest problem. It is the Gmail email service that seems to be affected the most, but you will be pleased to know that Apple is already working on a fix, but when it is released is anyone’s guess.
Normally when Apple would wish to update its Mail app in Mac they would just issue it as a standalone download, but because Apple is already working on OS X Mavericks 10.9.1, they could release it as part of that instead.
The new version of the Mail app is 7.0 with a build of 1822, compared to the one currently used my Mavericks users, 1816. According to 9to5 Mac the update is said to fix the Gmail issue and improve stability.
Apple employees and testers are now putting the updated Mail app through its paces and have been asked to pay particular attention to using Mail with Gmail, iCloud, sending and receiving mail. As well as Moving mail about, deleting, and much more.
The update is not part of a Mavericks update just yet, but because OS X Mavericks 10.9.1 is already in development, Apple could delay the public release of the Mail patch and release them as one. This would make more sense, but then again that all depends on how long it will be before 10.9.1 is ready for release.
Also See: iOS 9 OTA beta 3 update notes live