Creative Commons Share Alike 3.0
If an HTML message is not correctly displayed in Evolution it might be that the formatting of the message is specified as CSS. CSS is currently not supported by gtkhtml (the part that is used to display HTML).
This will likely be fixed in version 3.2 or 3.4.
For developers only: In future versions, Evolution will use WebKit instead of gtkhtml for displaying HTML. There is a branch named "webkit" in Evolution's code repository to test.
For missing characters in emails, see Character Encodings and Sets.