add a "prevent spam" sieve action for filters

[diroots]

Is your feature request related to a problem? Please describe.

sometime, users have mails classified as spam because of the spam filter used in the mailserver

using the 'mark as not spam' do not always work as expected, even if used, mails can still be flagged as spam

Describe the solution you'd like

We can use sieve filters to 'bypass' the spam classification

with sieve filters UI in snappymail, this actually works with the 'Move To' action, but it oblige users to create a filter that move to a particular subfolder of their inbox. in the Move To, the root INBOX is greyed and not selectable (expected, as it's goal is to move to a specific folder)

also, if, instead of using sieve filters UI provided with snappymail, we use sieve code, we can write this code and it works :

require ["fileinto", "envelope"];

if envelope :all :is "from" "someuser@example.com"
{
    fileinto "INBOX";
    stop;
}

but we can't have both scripts written from UI AND script coded to work at same time, and it oblige users to write sieve scripts themselves

the above tests work as sieve filters work at delivery time, when receiving mails, so it's applied before the mail is stored in a specific mailbox.

in the action list, we could add a new entry that could be called something like "Force unspam" or "Prevent spam flagging" that could be used to set this up, so users could use this to whitelist (based on conditions they define, as with other filters) and bypass the spam flagging

Describe alternatives you've considered

update in core snappymail sieve filters OR implement as a plugin ?

[the-djmaze]

When you use rspamd and dovecot, you can configure them in a certain way to interact.

1. When you mark as spam, rspamd will learn that as spam
2. When you unmark as spam, rspamd will learn as ham

See their documentation to configure it.

As for the filters gui: no, not at the moment due to compatibility with rainloop.
However, rainloop is dead and improved gui for sieve is already a feature request.

You could also have both sieve scripts active, the include rule solves that.
https://datatracker.ietf.org/doc/html/rfc6609.html

require ["include"];

include "rainloop.user";

[the-djmaze]

Oh, i forgot to mention an option in application.ini named sieve_allow_fileinto_inbox
Enable it and the INBOX is selectable.