Apple released OS X 10.8.5 update for Macs today, recommended for all Macs with OS X 10.8 Mountain Lion.

Connectikpeople has observed that, the update addresses issues with Mail, AFP file transfer performance, screen saver and more. This means as from now, issue that may prevent Mail from displaying messages is fixed. AFP file transfer performance over
802.11ac Wi-Fi has been improved. Apple also resolves an issue that may prevent a screen saver from starting automatically and finally improves Xsan reliability.

You can update by going to the software update utility on your Mac or pick it up from the Mac App Store.