Reading spanish special characters: ñ, ´, ¿, etc.

For several weeks, incoming emails in Thunderbird are not displayed correctly because special characters in Spanish are not recognized. The outgoing emails, on the other hand, do read well on my PC.
I have made a new installation of Thunderbird without adding my profile and only configuring the email account and the problem is the same.
The version of Thunderbird that I use is 60.6.1 for Windows Spanish (from Spain) with MD5 24f19cdee7a0ba3e0791f508753b11a7 and I have tested it in Windows 10 of 32 and 64 bits with the same result.
I have used all the possible encodings for formatting the emails and the result is always the same.
Is it possible that there is a bug in the application that caused this problem?
What can I do to solve it?
Thanks in advance and kind regards.