leefoo: If an email is currently unread - in bold font, then the right click option 'mark as unread' is auto disabled because it is already marked as unread. This explains why that option is not available.

re: settings Those are the correct settings in Options to mark immediately as read upon opening. I notice you also use the option - upon double click to open in a new window.

re: version being used You can tell what version you are running by selecting: Help > About Thunderbird

The current version is 31.6.0, which was due for release end of March, but there was a slight delay. I know it was definately available for update by 2nd April 2015.

I presume you have tried restarting Thunderbird. I'm also presuming you have the settings as per your image. So before doing the next test, please make sure the settings are exactly as your images in Options and click on OK.

Test: Please start Thunderbird in Safe Mode. Help > Restart with addons disabled

When TB has started in Safe Mode Left click on an email in the list, so it displays in the Message Pane below. Did the email in the list change to 'read' - not bold ?

Also test; Double left click to open in a new window Did the email in the list change to 'read' - not bold ?

If the email was marked as read - changed from bold to unbold - then there may be an addon causing a conflict. ReStart Thunderbird and it will restart in normal mode. Disable an addon one at a time and retest to see which one is the problem. It may need to be updated.

Report back on Safe Mode test results.

Thank you for your reply. I tried the Restarting in Safe Mode and disabling add-ons but nothing changed. Btw, it appears that I have no add-ons.

"When TB has started in Safe Mode Left click on an email in the list, so it displays in the Message Pane below. Did the email in the list change to 'read' - not bold ?"

--No, it did not.--

==

"Also test; Double left click to open in a new window Did the email in the list change to 'read' - not bold ?"

--Yes it did.--

=

Btw, I didn't think it was an add-on, because I hadn't "added on" any add-ons. :) But, it was worth a shot. :)

=

Would uninstalling and re-installing work? Would it save my contacts and messages? I ask this, because, about a year ago, I reinstalled Win7 and I did everything correctly (I'm pretty sure) to save them all, but the messages ended up corrupted and all of my contacts were gone.

again...thx

Lee

Please check to see if rebuilding the index fixes this issue.

Updated: Make sure you have this view: View > folder > All or Menu Icon > Folders > All

Right click on folder and select 'Properties' click on 'Repair folder' button click on OK

Select another folder and then reselect the folder which you repaired the index. Select an unread (bold) email, so it shows in Message Pane and report back on results. Did it become 'read' - unbold?

Toad Hall....again my thanks for helping.

Unfortunately, that did not help. I assumed I was to "right click" on Inbox, correct?

Btw, I created that dupe question, because, after I sent out 3 private messages (and the first two answered saying they couldn't help), I discovered how to ask an overall question (you guys don't make it easy, that's for sure) and even then wasn't sure it 'went'.

sorry.