Hi Mr Pix, not totally sure of the "sending" part, but if you go into the directory where the shelves are stored on you pc (make sure the custom shelf is clearly named so you can find it easily) you can just copy the mel file right out of the folder, if you don't know where to look here's an example of where mine are...
documents and settings\my documents\maya\8.5\prefs\shelves. Then copy the mel file of your custom shelve to your desktop,then if you want to e-mail it you could put it in a rar file and send it that way. Then they can simply extract the file and put it in the the same shelves folder on their machine. Hope that's helped a bit.