One substantial issue that has affected users after upgrading to OS X El Capitan is that Mail messages might be missing. In some cases it may be a few messages, while in other cases entire accounts have been emptied with no messages available. Sometimes this type of problem can be fixed by adjusting account settings to re-establish contact with your account servers, after which re-syncing will download your messages again; however, this does not always happen. Continue reading
Manage lost Mail messages after upgrading to El Capitan
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When you upgrade OS X, the accounts you have configured in the Internet Accounts system preferences should migrate and be just as usable as they were before upgrading. However, there may be times when calendars won’t load, e-mail messages may be missing, or you otherwise cannot access your accounts. While specific problems can be individually investigated, if they are nondescript and affect multiple accounts, you can try re-migrating your user account from a backup. 
Calibrating your Mac’s display will ensure the digital values in images are translated to display properly on the display devices you use, and is an important step anyone doing image editing and graphic design. To help with this, OS X has a built-in display calibration tool which supports both basic and expert modes for calibrating your display. These options are nothing new for OS X; however, in El Capitan Apple has made the calibrator’s expert mode hidden by default. 
Apple’s Retina MacBook Pros have a glass-covered display that has a coating of anti-reflective material to combat glare. However, some users have found that after a while this coating may separate, causing unsightly splotches that are most apparent when viewing darker content in bright lighting situations. If you are noticing these problems with your MacBook, then you may be in luck, as Apple has started a program to offer free replacements for the devices. 
Having long battery life is important for your iPhone, so it may be frustrating if you are seeing your battery levels dropping rapidly instead of giving you the 10+ hours usage you expect. In these cases, there are several things you can do to help and troubleshoot the problem, especially true if you have upgraded your iPhone or iPad to iOS 9, where new services can help you track possible battery drains. 
For the most part you will likely set up your Mac’s display in its default landscape orientation; however, there may be times when you might find it could be more convenient to have your Mac oriented such that its display is at a 90 or 180 degree orientation.
When you upgrade your installation of OS X, the OS X installer will attempt to detect and remove any incompatible software that may destabilize your system. However, there are times when such software may slip past Apple’s detection routines and affect your system. While often you can use troubleshooting routines after installation to manage such problems, on rare occasion these issues may prevent your Mac from booting altogether, leaving you with no ability to use your machine.