right click the folder, select properties and then the repair button. That re-indexes the mail.

Thanks, Matt. This did NOT do what I need. I still have 111 (I counted them since posting) messages with same subject line and date/time. So I'm guessing this is deeper than the indexing?

The message contents are different, so there are in fact the 111 original messages, but they are incorrectly labeled.

(Folder--local "Sent Items"--contains total of 331 messages, same number as original. Errant messages are part of a series I've sent out, and Subject of each starts with same content. They also go to several Bcc's. It's sort of a newsletter.)

So seems like I need a different path of import or a different re-indexing.

I've looked at help items for export/import, but they are from like TB 38, so I don't know how accurate they are. ( https://support.mozilla.org/en-US/kb/switching-thunderbird#w_importing-from-outlook-and-eudora ) Import seemed to work other than this folder (but I haven't gone through each and every folder--I have checked and found all folders have the right number of messages, but that's true for Sent Items also).

As a last resort, I might end up asking how I can modify Subject and date/time on individual messages and manually correct each one!

select one of the emails in Thunderbird, press Ctrl+U to open the message source. Is the correct subject actually shown in the Subject: header field? If not nothing is likely to fix it

Thanks again, Matt!

Okay, unfortunately, the errant messages have the same exact subject line and time stamp, or at least the two I checked do.

But I have a surprise! Based on your suggestion and my findings, I went back into Outlook, grabbed one of the 111 problem files, and looked at the source: Even though the Subject and date stamp are shown correctly, the source is WRONG!!!! The source has the same errant Subject and date stamp as was imported! I checked a couple more and found the same.

Okay, so re-importing is out. But stepping away from what I can do for a minute to what happened. I think I know: Since I've been sending this series to the same several people, I have created each new message by opening the previous message and selecting "Resend". I'm guessing that Outlook sees all the 111 messages as the same message repeated. (I've done this a few times with TB accounts also [Edit as New Message]; I'll have to look back at their source.)

Back to fixing: So okay, if I decide I can't live with 111 "identical" messages, is it possible to edit the underlying file? I make this to be:

[Identity]\[profile]\Mail\Local Folders\Outlook.sbd\Sent Items

And more importantly, if I do edit here, is there any kind of character count or coding within the file that will cause me to trash the file if I change it? (I tried this once with Juno mail, about 20 years ago.)

I might have a few messages in other folders with this problem, but those will be only pairs or triplets, so no worries.

Meanwhile, I now know that the present FB import function works, at least mostly.

Thanks again!

Okay so a follow-up here:

1. Fixing the data: I was able to save the errant messages to an MBOX file, edit that file, and re-import. This gave me a new/separate folder with the corrected messages. (I've only edited some of the messages, to test it.) I should be able to move these messages back to the correct folder and then delete the errant messages.

I've been able to use Outlook to show the messages with the correct Subjects and Timestamps, and match the Body to relabel the already-imported messages.

2. How TB handles my shortcut: Just as I was doing in Outlook, I opened a previous message, did [rt click] > Edit as a new message, and created a new message from the old. Once sent and stored in the local Sent folder, I looked at the header and it is correctly updated.

So thanks, Matt. We can consider this problem solved.