This sounds like a character set/encoding mismatch. The message is encoded in one format and Thunderbird is using another. This might be because the incoming message has an absent declaration, and Thunderbird guesses and gets it wrong. Alternatively, there could be an inaccurate declaration, so Thunderbird obeys this and gets it wrong again.

Another possibility is that Thunderbird has been set to override the encoding in the message.

Right-click an affected folder, select Properties, and make sure the "apply encoding..." box isn't ticked. If you can confirm that an encoding is not being declared in the affected messages, setting the appropriate fallback encoding here may also help. I think (but can't be sure) that messages are arriving using a Windows or ISO encoding and Thunderbird is applying Unicode. Or vice versa.

thank you...did not fix it tho. if I redo character coding for the email that comes in with the strange characters from Western to Unicode it fixes them.

but it wont hold that setting when I close out. strange.