re : Today, all attachments come in as winmail.dat files.

That's because the sender is using Outlook and incorrect settings. They should only be using those settings when they know they are communicating with someone else who uses Outlook eg like an internal mail. Advise them to set up Outlook correctly - even outlook advise this. Send them this link: https://support.microsoft.com/en-us/topic/how-email-message-formats-affect-internet-email-messages-in-outlook-3b2c0536-c1c0-1d68-19f0-8cae13c26722

There is an addon available: https://addons.thunderbird.net/en-us/thunderbird/addon/lookout-fix-version/ If you are having a problem with that addon then you need to duscuss that with the author.

re : PDF viewer is not compatible with my version of Thunderbird.

I use Adobe Acrobat and all works ok. What PDF viewer are you talking about? What OS are you using?

You say latest version, do I presume you are using 'release' version - did you install from here: https://www.thunderbird.net/

You could set to open pdf in a new tab using Thunderbird as a workaround.

Toad-Hall, THANK YOU! I'll contact the sender and have him configure outlook per the link you sent.

So far as the second reply, I'm using Windows 7, Acrobat Pro 11. (Yeah I know, I'm WAY behind.) I think the fix should work. If not, I'll keep working in it.

One interesting thing. My laptop is set up exactly the same as my desktop. Same OS, release of TB (91.9.0) and version of LookOut (fix version) 4.3 and it works flawlessly. I've done something to my desktop or TB on it, but Ill be darned if I can determine what I did.

Thanks again.