You're better off first trying to sort it out with the version you now have installed.

1. backup your profile data https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data#w_backing-up-a-profile

2. with thunderbird running go to help > troubleshooting > about:profiles ... there you will see the names of all the locations where thunderbird had stored data ... take a screen shot of this

3. Do you see "default-release" with "This is the profile in use and it cannot be deleted."? If so, at the profile named "default" click "set as default" and restart thunderbird. If not, post your screen shot here?

What are your results?

It's too late. Everything got trashed and I cannot sort it out. I suddenly have files that end in "-1". I copied the contents of its counterpart without the number into it and was able to get some folders back but all my archives are still now showing up, plus I still cannot send emails from all accounts on the same domain and SMTP server. Some accounts will send mail; some won't. I uninstalled the update and reinstalled the most current version I had been using so successfully and without issues for quite a long time.

I do not understand why my attempts to open my trusty Thunderbird failed because I did not have the update. I did not want the update at this time. I have too much going on. I just wanted my email. Now I don't even have that.

It's too late. Everything got trashed and I cannot sort it out.

I assume you posted here for a reason, as it is a support forum I would assume that reason was to obtain support. But from your description what occurred is not clear. One thing I will not discuss is "going back" I tried it and while I made it run it was a mess. You have enough issues without trying that particular disaster waiting to happen.

I suddenly have files that end in "-1".

The usual cause of such files with a number is file contention, that is Thunderbird fries t writew to a file, it is not available and it is therefore "replaced" with a new version with a number on the end. I have seen folks here with files numbers about all the way to 99, until they stopped having their anti virus scan files as they changed.

I copied the contents of its counterpart without the number into it and was able to get some folders back but all my archives are still now showing up,

yeah that does not sound like a good idea at all. Was Thunderbird running while you did this?

plus I still cannot send emails from all accounts on the same domain and SMTP server. Some accounts will send mail; some won't. I uninstalled the update and reinstalled the most current version I had been using so successfully and without issues for quite a long time.

So I guess not your stuff is a mess and your contacts are gone. That is why I said it was a bad idea further up. It is not a solution. It is actually only making things worse probably.

I do not understand why my attempts to open my trusty Thunderbird failed because I did not have the update. I did not want the update at this time.

As Thunderbird is not self updating for any existing users before 78.2 is released all I can ask here is how did you get an update. I have seen folks are installing all sorts of "Updater" programs that find and install updates for them. I have also learned that kaspersky anti virus has a module that has screwed a number of their users over with unwanted and unplanned updates. SO how did you come to get the update?

I have too much going on. I just wanted my email. Now I don't even have that.

And you attempts to fix the issue have almost certainly made things worse. SO how about we start again and this time you actually answer questions, provide information and undertake the functions asked.

I will start be asking you to do the following?

1. Open the menu > Help > Troubleshooting Information, then click Copy text to Clipboard.
2. Go to https://pastebin.com, paste the info from your Troubleshooting Information page, use the Create New Paste button to create a page containing your info, then copy the resulting URL (address) of the page created.
3. Open a reply to this post, and paste the link to your troubleshooting information you just copied.

Next, we'll need you to provide answers to the following questions:

• Does Thunderbird work in Safe Mode?
• Do you use anti-virus and firewall software? What is the version?
• Who is the email provider for whom you do not get mail/send mail?
• What are the error messages you see?

My personal feeling here is that your problems all stem from a single source. You anti virus product. But that is just a guess based on long experience with people not being able to get mail and generally having malfunctions after updates. for instance I would suggest you try the following before you discount the anti virus theory. Restart the operating system in safe mode with Networking. This loads only the very basics needed to start your computer while enabling an Internet connection. Click on your operating system for instructions on how to start in safe mode: Windows 10, Windows 8, Windows 7, Windows Vista, Windows XP, OSX

If safe mode for the operating system fixes the issue, there's other software in your computer that's causing problems. Possibilities include but not limited to: AV scanning, virus/malware, background downloads such as program updates.

I may have time in a week or so; work deadlines are extremely high pressure right now and my nonprofit organization cannot be suspended so I try to keep it running by going into each individual email account directly on the mail server thru a web interface. Plus I plan to switch out the HD for a solid state, which has been sitting ready for about three months but I've not had time.

I already uninstalled the 78 version and reinstalled the one I had been using most recently. I am making everything worse, so I am probably going to leave it all alone and install MailBird or something else to get me through rather than try to sort through the disaster that the Thunderbird upgrade did to my system.

I have not had scanning software running for a few weeks. I do not know if I had Thunderbird running when I overwrote the contents of the file-1.