drag and drop. open the folder. Press Ctrl+A to select them all and drag them back to your sent folder.

However I would suggest moving 5000 emails out of the sent folder as a very positive thing. Why would you not want to do that?

Thanks for responding, Matt!

I'm on a Mac, if that makes any difference. Here are some other details...

The folder I archived was under "Local Folders" in the sidebar on the left in Thunderbird. I used to be able to easily look through the emails I'd sent in the past, and now I can't do that.

I found a large file, 2.2 GB file, located in my Thunderbird Profiles (deep into the library), within "Local Folders", and the time it was modified corresponds to when I did the archive...so I imagine that is the archive file. It opens with TextEdit. It is a lot "clunkier" to use and find stuff than the way it used to be...that's why I'd like to go back to before I archived it.

So to return it to the way it was before, are you saying all I have to do is open the big TextEdit file, select all, and drag and drop onto the Thunderbird Sent file in Local Folders? Will that do it?

Really appreciate the help, Matt, thanks for your patience with this not-too-computer-literate old guy.

You should have an archive folder showing under Local Folders. You view messages in that folder just like you do any other folder in Thunderbird. No need to be browsing your computer file system and messing with text files.

Thanks Airmail, I really don't want to mucking around in the computer file system at all. Maybe this picture of the sidebar in Thunderbird will help explain things. The folder I archived was the "Sent" folder under "Local Folders", and I just want to return all the archived emails to that folder, the way it used to be.

what happens when you open the say 2017 folder in the archive. it should show all the archived mail from that year.

Likewise 2018 should show all mail for the year.

Depending on your setup of the archive, it may have retained the original folders in the year folder. but that is a user setup item. for instance when I archive mail it goes into a year folder, with a sub folder the same name as the source. So I have say a 2018 archive that contains a sent folder

Matt, Now I'm red-faced and embarassed...because, yep, all the sent emails were magically added to the existing yearly folders. Easy to navigate and read, easy to use the filter to find specific emails, etc, etc, etc. So, false alarm on my part, and I totally overlooked the obvious. Thanks for helping me to figure out that there wasn't even a problem, and now I'm glad I archived the sent emails...just as you said in your very first response. Big Thanks to Matt and Airmail for helping me out!