This surprises me. My experience has been that the Thunderbird updater won't suggest a version that's incompatible with the OS. Specifically, the latest version that runs on Windows 7 is 115.18.0. On my Win7 computer, when I check for Thunderbird updates, it always says that it's up to date. Also, if I try to install a later version than that, the installation stops with the error message, "Sorry, Thunderbird can't be installed. This version of Thunderbird requires Microsoft Windows 10 x64 or newer."

What version were you previously running and what did you get updated to?

When I now try to run thunderbird.exe I get the following: "C:/Program Files/Mozilla Thunderbird/thunderbird.exe is not a valid Win32 application."

As the executable can't run, is there a way to retrieve the version numbers somewhere in the Program Files?

This executable was auto installed at 9:44 PDT today (10/32/2025). I don't know the version numbers, but it looks like the last update was 5/12/2024.

You can find the version by locating the file "C:/Program Files/Mozilla Thunderbird/thunderbird.exe" with Windows Explorer by right-clicking on it. Then look at the "Details" tab and then "Product Version".

Yours is the 64-bit version of Windows 7, isn't it?

The danger of downgrading from a later to an earlier version is that the later version may have changed something in your profile that makes it incompatible with the earlier version. However, it sounds like you were never able to even start the new version, so your profile should be intact. That's a good thing. You may be able to just uninstall the later version and re-install the older, preferred version. But let's find out what's currently installed.

Eventually you will want to install the last Windows 7-compatible version, 115.18.0esr. You can get that here (assuming you want the US English version):

https://releases.mozilla.org/pub/thunderbird/releases/115.18.0/linux-x86_64/en-US/

I am very old school, running a 32 bit Win7 OS. The "Properties" on the executable gave me lots of information.

"Details"

 Product version 128.14.0
 Modified 10/31/2025 9:44 am

"Previous Versions"

 Previous Version
 thun 1/16/2025 8:35 am
 115.18.0 (32-bit)

The latter found in the restore point. I double clicked of that entry and it ran, abit without any libraries or data files as it isn't installed. I really really want it back proper with access to my old emails.

Can you install the last version for 32-bit W7?

https://archive.mozilla.org/pub/thunderbird/releases/115.18.0/win32/

It's Halloween - I'll pick this up tomorrow - thanks