In fact I now know a lot of things which I didn't know about fonts, and I thank in particular Christopher Handy from the list, who knows all about these things being an essential part of his present job.

I now have all the technical informations to try and solve this question-marks issue.

In fact, seen that this problem occurs to me only in the emails I receive from this list (never on the web), and since I do receive them in digest form, I will first try the suggestion of Dominik Wujastyk and in case it works I'll point it out to the list administrators.

Thank you all again, and let's go back to subtler questions!