When Outlook.com was first made available as a mail domain back in 2012, I immediately went and registered a few accounts, figuring that it would become a high-profile service pretty quickly. One of them I have almost never used, and in its eight-year lifespan it's received...(checks)...7 emails. All of which were from Microsoft.
That account is still up, though, and I don't believe I've checked it from the website itself in years, although it is one of the accounts I've linked to my Outlook app. So the mere act of polling an account for email might be enough to be considered "active".
I haven't checked what would happen if I did the same polling but only used Thunderbird instead.
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."
That account is still up, though, and I don't believe I've checked it from the website itself in years, although it is one of the accounts I've linked to my Outlook app. So the mere act of polling an account for email might be enough to be considered "active".
I haven't checked what would happen if I did the same polling but only used Thunderbird instead.