Get a Gmail or similar web email provider account and then you are not beholding to any particular provider. Doesn't take too loing to get your contacts using the new address and then you are away laughing.
I am not with Slingshot but imagine if you are not a customer then your ISP email address will not be held for you. It's not transferable and they wont provide the service for free.
Always be yourself, unless you can be Batman, then always be the Batman
exact reason I suggest ALL people avoid their ISP emails like the plague.
VF charges me for paper bills and sends the pdf ones to their provided email address (dunno if it's still the case) presumably to get me using their ISP email and having another hook to hold me to them....
but TBH it was easy enough to just set it up to redirect to my 'catch-all' webmail account and deal with it from there anyway.