[hayyyyydos]

> How would you whitelist things in your regular IMAP client? Manually moving things to the IMAP Inbox and which then marks them as whitelisted somehow?

That's exactly how you'd do it, and the functionality definitely exists - all handled on the server side. See: learning spam from ham by dragging to/from the spam folder.

https://wiki.dovecot.org/Pigeonhole/Sieve/Plugins/IMAPSieve

[dewey]

I wasn't trying to say that this method would be hard or impossible to build, but it's hard to use for the average user. Moving mails around on mobile apps is already annoying enough (At least in the iOS Mail.app)