Reinstall Thunderbird and hope the reinstall resets the MAPI setting which have apparently been set to point to microsoft... perhaps you used outlook once recently, that will do it?

Thanks so much for replying, Matt. I should have mentioned that I'd uninstalled Tbird and installed it again, which didn't fix the problem. I did open up Outlook to see what would be involved in switching over to that--which I am loath to do--but I never used it to receive or send any email. Do you know if there's a file I can get access to (I have a hex editor, if that's helpful) where I can "correct" that MAPI setting you mentioned? And also to what MAPI should be set? Again, thanks for replying! Dave

The information is in Windows registry for mapi, test if it is wrong by trying to send an email from windows file explorer.

I think I recall some sort of discussion years ago about office product being hard coded for outlook only. One of those vendor lockin things.

Yep looked it up. Vendor lockin https://support.microsoft.com/en-us/office/email-a-document-from-microsoft-office-2754aa3a-929b-4dc6-b400-28fbf91c0d77

Again, thanks, Matt. I did try sending a file from windows file explorer, which launched a Tbird email, which then was sent successfully. As you surmised, and as the link confirms, one must configure Outlook as the default email app to use the feature of sending from WITHIN Word or Excel. But I don't understand why I could do that for years and now all of a sudden I can't. Weird. Since I'm unwilling to make Outlook my default email app, I guess I'll just have to close the Word or XL file when I finish editing, and launch a Tbird email, attaching said file for its recipient. I hope you and yours have a wonderful holiday season!

There's a bit more to the step of reinstalling TB. First, find out if your Word and Excel are 32 bit or 64 bit. If they are 32 bit, TB must also be 32-bit. Once you confirm the TB and Office apps are MAPI-compatible, download the full installer for the exact same version of TB that is currently installed, choose the Advanced setup and set TB as the default email client, don't run TB at the end of setup, then restart the computer. See if a file can be sent from Word or Excel through TB.

https://support.mozilla.org/en-US/questions/1323685

Thanks, SFH; I'll try that tomorrow, since I'm fading fast..... Dave

Good morning, SFH--- Since Google says that my MS Word 2007 is 32-bit, I googled "32-bit Thunderbird" and clicked the download button that came up at the link. I did NOT launch Tbird during the install. Re-booted; tried sending a file from within Word; same failure. And now I don't even see Mozilla Thunderbird when I click the leftmost window in the taskbar and scroll through the programs, but I know Tbird is installed because it works okay by itself. I think this is wasting your time and mine, so let's just give up on it. I'll close the file, create a new email & attach the file. Best regards, Dave

If you do not want to launch Outlook and MS Product Word/Excel will only launch Outlook, then you could con it into believing Thunderbird is Outlook.

In Windows search type: Registry and select 'Registry Editor' to open.

Locate: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\App Paths

   Do you see an 'Outlook' or 'Outlook.exe' option ?
   If yes:
   Leave as is but you will need to modify what it does later.
   If no:
   Right click on 'App Paths' and select 'New' > 'Key'
   Name it: outlook.exe 
   This will create:
   HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\App Paths\outlook.exe 

Locate: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\App Paths\thunderbird.exe

   On the right it will have two ab listed names (Default) and 'Path' both of type 'REG_SZ'
   Double click on 'Default' name to open 'Edit String' window.
   Do not edit anything.
   Copy all the 'Value Data' - highlight all text, right click and select 'Copy'
   click on 'Cancel' to close as you do not want to save anything. 

Locate the Outlook you found or created earlier: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\App Paths\outlook.exe

   In 'Name' column it will say Default.
   Double click on 'Default' to open the Edit String window.
   In the 'Value Data' text box, Paste in the copied text - right click and select paste.
   click on 'OK' to save 

If this 'Outlook'/Outlook.exe was already in existance, you will have seen on the right it will have two ab listed names (Default) and 'Path', but if you had to create 'outlook.exe' then:

   Right click on the App Paths\outlook.exe and select 'New' > 'String Value'
   Name it : Path 

Locate again: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\App Paths\thunderbird.exe

   Double click on 'Path' name to allow you to 'Edit String'.
   Do not edit anything.
   Copy all the 'Value Data' - highlight text, right click and select 'Copy'
   click on 'Cancel' to close. 

Locate again: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\App Paths\outlook.exe

   In 'Name' column it will say Path.
   Double click on 'Path' to open the Edit String.
   Paste in the copied text - right click and select paste.
   click on 'OK' to save 

This should result in you having both a 'thunderbird.exe' (already installed) and a 'outlook.exe' (you newly created) in 'App Paths'

• HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\App Paths\outlook.exe
• HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\App Paths\thunderbird.exe

When you select 'outlook.exe' it should look identical to when you select 'thunderbird.exe', so both are the same with the exception of the 'App Paths' name.

Your management software program will look for App Paths\outlook.exe and find it, but it is tricked into using thunderbird - (assuming that MS program is auto searching for outlook.exe).

Thanks, Ms.|Mr. Hall!

I'll give that a try soon and letcha know!

Best regards, Dave

Good morning, SFH--- Since Google says that my MS Word 2007 is 32-bit, I googled "32-bit Thunderbird" and clicked the download button that came up at the link. I did NOT launch Tbird during the install. Re-booted; tried sending a file from within Word; same failure. And now I don't even see Mozilla Thunderbird when I click the leftmost window in the taskbar and scroll through the programs, but I know Tbird is installed because it works okay by itself. I think this is wasting your time and mine, so let's just give up on it. I'll close the file, create a new email & attach the file. Best regards, Dave

The 32-bit version for the current release is available here:

https://www.thunderbird.net/en-US/thunderbird/all/

For other versions: https://archive.mozilla.org/pub/thunderbird/releases/

Uninstall the existing 64-bit version before installing 32 bit exactly as described above. The profile folder with your data is not affected.