The OS X Yosemite v10.10.5 Update is recommended for all OS X Yosemite users.
The OS X Yosemite 10.10.5 update improves the stability, compatibility, and security of your Mac, and is recommended for all users. This update:
Improves compatibility with certain email servers when using Mail
Fixes an issue in Photos that prevented importing videos from GoPro cameras
Fixes an issue in QuickTime Player that prevented playback of Windows Media files
For detailed information about the security content of this update, see Apple security updates.