Am I responsible for backups ultimately? Absolutely. Will I trust Mailchimp in the future for my own projects? Not very likely.
> We're afraid the TinyLetter data is no longer available
could perfectly mean: the backups we keep for one year are encrypted in case of legal trouble, but we require a legal action internally before them to be worth reaching out.
If it makes you feel better, deliverability people will tell you a list that’s been sitting with no sends for a year or more quickly becomes worthless due to list rot (abandoned emails, expired domains, job switchers, people who forgot you exist and will mark spam/unsub, etc).
When you send to an old untouched list, it can tank your domain rep in Gmail since the algo sees tons of bounces/unsubscribes/negative signals. They basically assume you’re a spammer. So it probably would have been a PITA to warm that list again anyways. It’s shitty that gmail incentivizes bulk senders to be annoying and send a lot, but it is what it is.