It's comfortably running within GAE free quota so even if we disappear it should be up and running ... Gotta pay that domain for max years though ;)
Good question, thanks!
You are in the least safe position possible. You're on a free Google service. In spite of the longevity of a few of these services, those are shut down all the time.
You say:
> To make sure you are well and sound, Cronu will charge your card a dollar a month.
I would insert "and to ensure your message remains available", as written this feels so inauthentic as to be mildly offensive.
And then take that dollar a month from myself and from a few others, and spin up some paid instances. Pick a couple hosts that are likely to be around for a long, long time, and get a box from each, and make your service redundant. Show that you've paid for service from these providers and have paid up for the next 10? 50? 100 years. Register cronu.com for the next 10? 50? 100 years (this expiry date is easily verified with whois) because you obviously can't send email from cronu.com if your domain registration expired. Right now, your expiry is in September of next year.
Paying for these instances is what distinguishes you from a free monthly dead-man-switch email and makes you worthy of receiving that dollar.
We do have budget and will be paying once quota is depleted (can't wait for that moment) but so far (and in case of our disappearance) free should sustain the minimum viable service levels (aka delete account).