The evolution welcome message contains characters which are rendered as hex boxes with the default FC font setup.
What numbers are inside the hex boxes? This will help determine which font is missing or whether the text encoding has gone wrong.
On my Fedora machine I see a [0020] hex box after each bullet in the New Features section of the message.
0x20 is the space character. The space character should normally be display ok, as it is encoded the same way whether it is UTF-8 or latin1 or iso-8859-x. Most probably the issue arises from the bullet character; my guess would be that the bullet character is a Unicode character, however there is an encoding issue in that fragment of Evolution's code. Can you check with Character Map that 0x25CB or 0x25CF are available in FC6t1? It appears that the stylesheet of the default e-mail uses those Unicode characters. I use Ubuntu at the moment and I am able to view those characters as my system font supports those Unicode ranges. To be able to rule out evolution encoding problems (because they are unlikely as in other distros it works), you can try to install the DejaVu fonts and view the default e-mail again. See http://fedoraproject.org/wiki/Fonts/DejavuFeedbackCall for instructions. The default e-mail is found at /usr/share/evolution/2.6/default/C/mail/local/Inbox (Ubuntu).
Hmm, this no longer happens for me in rawhide.