When trying to open an attachment with Thunderbird, below error message appears on your screen:
[Thunderbird] error message: "Unable to save the attachment. Please check the filename and try again."
This is due to a forwarded message that itself contain an attachment which however generates a bug under thunderbird. This is actually being worked by Thunderbird team which will be corrected for the future version.
Below is a temporary proposed solution
Click on View and then View attachments in messages .