If IMAP only usage was considered inactive I’d have lost my gmail and hotmail accounts over a decade ago.
Startup idea: SaaS that you register you email addresses and periodically does an IMAP request to keep them active. Premium tier would provide actual archiving of your emails.
If it wasn't for the "this service would need access to my email account creds and therefore to all my mail" showstopper...
A distributed service where a group of people all have their own service to "ping" their personal "important accounts", and which accept federation with friends or other users of the service, so if your server/vps/serverless/whatever platform instance goes down your pings still happen from your connected servers.
Elevator pitch: "Like IPFS, but for cron jobs calling curl."
Startup idea: SaaS that you register you email addresses and periodically does an IMAP request to keep them active. Premium tier would provide actual archiving of your emails.