Mavericks may have brought a number of notable improvements to OS X, but Gmail integration was certainly not one of them. Users of Google's email service might've encountered an unpleasant surprise when they upgraded their operating systems to Apple's latest, as the changes to Apple Mail appeared to be incompatible with how Gmail worked. For background, Gmail apparently has a rather unorthodox method of using IMAP, so you needed to set up a roundabout method that prevents Mail from downloading every single message from Gmail twice (Basically, you had to tweak your Gmail settings so that "All Mail" is hidden from email programs).
Mavericks, however, broke that workaround, so users of both Gmail and Apple Mail ended up suffering from bloated inboxes. There were other issues too, like the inability to organize mailboxes and unread message numbers that are totally off. Thankfully, however, Apple has just released an update that fixes all that. The release states that it "fixes an issue that prevents deleting, moving, and archiving messages for users with custom Gmail settings" and "addresses an issue that may cause unread counts to be inaccurate." So for those who've bitten the Mavericks bug and want a Mail app that plays nicer with Google's email, you should definitely hit that update button right about now.