Once had Optimum (the ISP) do this to a business I was working with. Just yeeted all their emails account and their contents and all backups thereof one day. Declared it was because no user on the account was accessing their email via the webmail system so all the email was nuked for inactivity. IMAP and POP do not count, apparently.
Short version, do not use Optimum unless they are the only option, and if they are the only option seriously consider moving to fix that.