Sitx files are the most unreliable files I can think of to send out... unless you're sending them to someone who is using OS9 and even then .sit is much more reliable.
If I have to email or FTP some large files, I either zip them preserving the resource-forks, or if I know they're going to a Mac OS X user, I make a compressed disk image of the project folder by dragging the folder onto the Disk Utility icon in my dock. Disk images preserve everything just so, including fonts and their resource forks.