I didn’t answered to your entire previous message yet, because I’m just re-learning all rspamd config I’ve forgotten while ill. Actually I even have some difficulties to understand what I’ve previously done 
Yes, one need to enable backports on Debian Buster
Sorry I didn’t understand
Rspamd 2.7 is available in Buster backports, 3.2 in Bullseye backports.
The learning can be setup as user based or server based. I think that if we setup it as user based we don’t really car whether it’s “real” Spam or just an email the user doesn’t want to receive. It’s the same action that we want in the end → go to Junk !
And yes, the learning is mainly about what the user wants, not what the user doesn’t want.
Don’t forget multi-user case. With a lot of users, each ones peculiarities concurrent themselves and there is no problems, but if you have fewer than a dozen users, you may break Rspamd spam detection because of 2-3 users adding normal emails in Junk folder. See Usage of fuzzy hashes
Server based spam detection must be trained and serve as a basis, while user’s own email client can detect user’s spam. But training Rspamd on a user Junk folder? I don’t know.
Some webmails comes also with bayesian spam detection, is it enabled in
I’m not sure to understand your question “is it enabled in Yunohost”
Is webmail spam detection working in current yunohost ? I didn’t checked.
Desktop email clients comes with spam detection too, where spam emails goes in Junk folder. Hence, shall we expunge Junk folder from server side? I don’t know
Same, here we don’t really care if the user voids his Junk box or not, or if his desktop client does it on a regular basis → we do it server side as a default, and everything else is a double fence (used or not). I don’t like client side based actions personnally.
Just think the opposite: a user folder should’nt be expunge by a server process.
I think that a Sieve rule on email age is better and can be overwritten on a user basis.
What could be Postfix, Rspamd or Milter errors messages, related to Junk folder, if user update its content from webmail or desktop or mobile client?
I didn’t understand that question ? IMAP is designed to be a client - server mechanism, so if the server does some actions they will be mirrored by the client, and vice versa
Yes. But IMAP is for Postfix, not Rspamd. I have the real case of a client adding some emails from another account like Yahoo or Gmail, in his Yunohost account’s Junk folder. Sometimes he can see errors messages. I didn’t investigate yet, but I’m concerned that the user was annoyed. Anyway this is mainly a question for Rspamd developers.
