I use Mountain Lion.

How do I prevent Mail.app (6.0) from marking a message as read automatically, just because I have looked at it in the preview pane?

2 Answers 2


You can change the mark as read delay to a great value, for example 30 seconds, by typing the following in the Terminal:

defaults write com.apple.Mail MarkAsReadDelay 30

(NB: A value of -1 will disable marking as read from Preview if the preview window is hidden. Tested on Mail 5.2/OSX 10.7.4)

  • Do you need to log out and log in again? I executed that in Mac OS X 10.8.4 but no effect. I doubt they removed the ability to do it even if it's not documented. Sep 20, 2013 at 23:34
  • 4
    This don't work in Mavericks
    – MiPnamic
    Jan 14, 2014 at 19:19

An other way to do do (without using the Terminal), is installing TruePreview. It's an 3th party app which allows you to do exactly what you expect.

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Do check for a recent version of TruePreview as older versions don't work well with Mountain lion.

  • The defaults write isn't being recognized by Mail.app in Mountain Lion. Recent versions of TruePreview weren't working either, but the latest build now works.
    – sprotsman
    Aug 21, 2012 at 17:33
  • The latest release 1.8a4 supports ML - christianserving.org/project/truepreview/releases Aug 24, 2012 at 16:56
  • I don't want to install that plugin though. What defaults write command will work in ML?
    – stantonk
    Dec 4, 2012 at 18:31
  • both links are now dead...
    – patrick
    Jun 3, 2018 at 0:43

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