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 ).
I’ve been trying to download this for a bit now – but all I get are SourceForge errors and empty file lists. I even tried grabbing the source and I simply get blank pages.
Were you actually able to get this downloaded?
Seems to be a general problem with SourceForge; I’m still getting a “400 Bad Request” page trying to download the latest version of phpMyAdmin.
PS: Maybe this trouble will encourage the developer to host TruePreview elsewhere; SF isn’t a popular choice for OS X projects.
OK I just got the SVN checkout and am building it now.
http://download.pocketinformant.com/Mac/TruePreview.mailbundle.zip
Alex, yes, I was. But that was before I blogged about it ;-)
Thanks for posting an alternative. I’ve linked to it in the main post. I hope that’s OK.
Yeah, that’s fine. Its why I posted it in comments. I mean I guess I’ll see how much traffic that actually hits, but I think it should be OK.
SourceForge downloads are working again.
Well darn, this sounded so promising.
Yes, you can configure a time delay so that simply selecting the message doesn’t mark the message as read, there’s nothing you _can_ do (short of the contextual menu selection, which is a hassle) to show it as read. I would have thought that double-clicking the message (to open in its own window) would then change status instantly.
I’d want the ability to travel up and down the list of messages without disturbing their status, but when I actually _do_ read a message (either by double-clicking or by scrolling through (with mouse wheel) the message in the Preview Pane) I want the status to change without having to wait for my pre-configured time to elapse. That’s more in line with how Eudora allows for timed status change configuration.
I’m told that this app has a 2 digit delay field to prevent the email being marked as read immediately. Is there a way to prevent it being marked as read at all unless I specifically open the email?
I use Mail-ActOn, which provides this functionality as well (but not for free, of course)
> there’s nothing you _can_ do (short of the contextual menu selection, which is a hassle) to show it as read.
What about using the Shift-Command-U shortcut (for Message > Mark > As Unread)?
> Is there a way to prevent it being marked as read at all unless I specifically open the email?
Do you mean when the preview pane closed? Seems like a bug if TruePreview is marking messages as read when it is.
just wanted to say… nice to see you back!
Hi there. Just updated to Snow Leopard.
True Preview does not work with Snow Leopard, any ideas of forseen updates and times?
Thanks.
Hi…nice to see you back.
Snow Leopard would be so much nicer with a true preview in Mail.
Just downloaded TruePreview and love it. Here is a quick update to questions in the other comments:
1) Now works with Snow Leopard
2) There are now additional options including when to immediately mark a message as read
3) The SourceForge page tells you to go to the developer’s website for download
Joe@ — thanks for the updates. I’ll check it out. Might be worth an update post.
TP 1.2 is compiled Intel-only:
http://christianserving.org/content/truepreview-1-2-released#comments
… and I haven’t gotten a response from the developer about it.
Broken in 10.6.2 released yesterday
TruePreview 1.3 is out. Unfortunately it’s still Intel-only and the developer hasn’t acknowledged my messages asking if there will be a Universal version.
Great utility! Works perfectly for me on 10.6.2. Nice touch with per-account customisations too.