Found a solution at https://forums.developer.apple.com/thread/14502 Per user Max108: Normally, your change to default email client is saved by LaunchServices, but that database can become corrupted. You can reset the database with the following command in Terminal (copy-paste the whole thing): /System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/Support/lsregister -kill -r -all local,system,user OS X will have to re-learn your preferred non-default apps for opening different types of files again, but it may fix the issue. That did it for me.