A quirk of the sup email client is that it doesn’t sync back changes like deletes to mail sources. “Deleted” messages are only flagged and hidden from the user.
A few minutes ago, for the first time in around a decade, I emptied my email inbox. I’ve been steadily whittling it down (or at least holding the line) for the last few months: catching up on mailing lists, responding to outstanding emails, admitting there’s some things that are so old I’m not going to respond to them, and moving work items onto a proper to-do list. So I have an impressively boring screenshot: