Hi, Brennie,
I don't think I can help you. The 3D printing services I've used have a web site, and on the web site is a button to upload an STL file. You click the button, choose the file you want to print, and it is uploaded to the site.
I don't know what service you're using, what you're trying to email, or what email program you're using.
With more details, a screen shot of the problem, etc., I might be able to offer advice.
-David