Jim Riggs has long been frustrated by Mail.app’s lack of options for previewing messages. So he has written the TruePreview plugin to fix it.

He writes:

One of the most common shortcomings/omissions/bugs/failures in Mail is the inability to truly preview messages. If the preview pane is displayed in the message viewer window, as soon as a message is selected and displayed, it is marked as read. Most every other e-mail client on the planet provides an option to delay marking messages as read.

TruePreview installs itself as a classic plugin bundle in your ~/Library/Mail folder.

It provides a new tab in Mail’s Preferences in which you can set a default time delay in each of your accounts for messages to be marked as read:

A very nifty piece of work!

Jim has tested this on the most recent version of Mail.app in 10.5.6, but is keen to get feedback from users with other configurations.

The plugin is open-source (BSD licence) and can be found on the SourceForge site (UPDATE: Or, if you are having problems with SourceForge, try here ).