There is a tutorial on how to do this here :
But it didn’t quite work for me. When I checked the actual message by signing in to my network it was different then the fields described in the Ning tutorial. So I did some research. This is what I did to change the automated email.

Log in as admin. Go to Language settings and choose the translation. For me it was Dutch. Then, on page 16 ( or perhaps for other languages page 15/17 ) there are four special textfields. Each of them has a subtext, which in Dutch reads “Deze tekst is voor het welkomstbericht”. The original English for that would be “This text is for the welcome email”. It’s those fields right there that needed to be altered to get a different automated email.

ning translation for email