Change Mail Apps “Mark As Read” Behavior in Mac OS X

Have you ever noticed that Mail app registers a message as “read” after it has been clicked? The automatic “mark as read” feature makes it easy to quickly skim through a bunch of emails, but Mail doesn’t offer much control over the the delay for when messages are marked read.

Adjusting Mail Mark As Read Behavior from the Command Line

If you’d rather not add a plugin to Mail app, you can also do some of this through the command line with defaults write commands, if you’re comfortable with that. Launch the Terminal

Set the delay to 2 seconds with the following:

defaults write com.apple.Mail MarkAsReadDelay 2

Replace the two on the end with any number to change the delay to that many seconds. You can also remove the delay with the following defaults write command:

defaults write com.apple.Mail MarkAsReadDelay 0

Return to the default setting with the following defaults delete command:

defaults delete com.apple.Mail MarkAsReadDelay

Change How Unread Mail is Managed in Mac Mail with TruePreview

Another option is called TruePreview, it’s a free Mail plugin that gives you control over how Mail app handles messages and their read behavior. With TruePreview, you can set messages to mark as read after a delay, disable the automatic mark as read feature completely, or restore to default settings, it also allows for these customizations to be made on a per account basis, allowing for read behavior to change depending on email addresses.

• Quit Mail app
• Download TruePreview (scroll down for latest versions) and run the installer
• Launch Mail.app and open Preferences, click on the >> arrow and select “TruePreview”
• Adjust the Mark as Read settings as desired

TruePreview works with Mail app in Mac OS X Lion (10.7.3) and earlier. If you want to uninstall the plugin for some reason, it can be found at:

~/Library/Mail/Bundles/TruePreview.mailbundle

Deleting that folder and restarting Mail will uninstall TruePreview.

Removing the delay with these latter commands seems to only impact Conversation view, according to Macworld.