Earlier quoted context omitted.
I will be honest, I don't even use email client :/
True, I suppose most people use Gmail or one of the other major email providers through a webmail interface. I haven't been able to get Gmail or Hotmail to display threaded messages the way they're displayed in Thunderbird and they tend to display messages using a variable width font. In that context, reviewing code would be difficult, if not impossible, to do via email.
Just send out email in HTML format with the code portions set to fixed width font and syntax highlighting already applied. Should display just fine in GMail.