Feature Request: Implement Quarantine fine-tuning

[Habetdin]

Summary

Currently the Quarantine stores messages based on a fixed set of taken actions:

mailcow-dockerized/data/conf/rspamd/local.d/metadata_exporter.conf

Lines 56 to 58 in 37beed6

	if action == 'reject' or action == 'add header' or action == 'rewrite subject' then
	return true
	end

However, for any action other than 'reject' an extra copy of the quarantined message is still delivered to user's Junk inbox.

From a user perspective: you check your junk folder, see a ham message and move it to your Inbox. rspamd sees this and learns. The message remains in the quarantine queue.

From an admin perspective: you check the quarantine queue, see a ham message and release it to the inbox. The message is still in the user’s junk folder, but now also in the inbox.

If both the user and the admin do their own thing: user moves email to inbox, admin releases email because it’s not spam, the user has two identical emails in the inbox.

So either junk shouldn’t be in the quarantine queue, or be removed from there on user action, and vice versa if the admin releases an email to the inbox, it should be removed from the user’s junk folder.

A possible solution is to be able to individually configure for each user exactly what to keep in quarantine and what not.

Motivation

Additional per-user settings would help to control the Quarantine workflow. As for now, the only related settings the users have are Quarantine notifications and Quarantine notifications category, which is insufficient to solve the Quarantine/Junk issue.

Even without per-user Quarantine settings we should think of fix for the duplicate messages issue because in current state admin and user could mark the same message as ham and spam at the same time, which is weird.

Additional context

Rejected messages are stored in the Quarantine. That's expected behaviour.

And the other junk messages are both delivered into the Junk folder and stored in the Quarantine. Delivering such messages from Quarantine to Inbox duplicates them.

1. If user keeps original copy in the Junk, what would be the result of Rspamd Junk-learning?
2. If user marks original copy as ham (moves it to Inbox), is there a way to avoid delivering an extra copy of the message from the Quarantine?

[DerLinkman]

Sounds good! Feel free to open up a PR for this.