Moving this from a downstream bug report:
https://gitlab.gnome.org/GNOME/evolution/-/issues/2388

Unfortunately, this is reproducible in Evolution, but I do not know what settings this requires to reproduce in a test app, thus steps need Evolution. Reproducible with Evolution 3.48.x and webkit2gtk4.1-2.40.3-1.fc38.x86_64.

Steps:
a) download and install https://downloads.sourceforge.net/project/mscorefonts2/rpms/msttcore-fonts-installer-2.6-1.noarch.rpm
b) open Evolution and in Edit->Preferences->Mail Preferences uncheck "Use the same fonts as other applications" and then set the "Standard Font" to "Calibri Regular  10" (the font size is important, it seems)
c) import into Evolution a test message https://gitlab.gnome.org/GNOME/evolution/uploads/55c7e5b2095132dc599004999d1bcd6e/eml.eml
d) select/view the message

Actual result:
some letters are missing, as shown for example here:
https://gitlab.gnome.org/GNOME/evolution/uploads/d6085d14f6793dfb756df35b7c72a647/Image-VDS271.png

Expected result:
should show all letters, like here:
https://gitlab.gnome.org/GNOME/evolution/uploads/1bfa099a34cb1833b9bb986ad06efa5b/Image-YALF81.png

Notes:
* Interesting is that the letters are there, I can select the white spaces (they are still empty after selection) and when I copy&paste the text into an external application the text is pasted in complete, no character is missing.

* Changing font size from 10 to 11 (or other) points in the Edit->Preferences->Mail Preferences makes some letters visible.