Enable Substring Search in Dovecot

[stephdl]

Issue Description
Currently, when using Dovecot with the Flatcurve plugin, we rely on the prefix-based search to find emails in clients like Roundcube. This follows a "Google-like" behavior.

However, we would prefer to also allow substring-based search to improve flexibility.

Expected Behavior
Searching for first should find first.user (prefix-based, current behavior).
Searching for user should also find first.user (substring-based, desired behavior).
Proposed Solution
Enable the substring search feature of the Flatcurve plugin by introducing an environment variable:

📖 Dovecot Flatcurve Substring Search

Alternative Solutions
Educate users to write full search terms for accurate results.

See Also

• NethServer ns8-mail v1.5.2
• https://mattermost.nethesis.it/nethesis/pl/i8tfrmzm3f8pjqu4w47k6hhowe
• https://mattermost.nethesis.it/nethesis/pl/qg686qdjctgjubcpq5mxmtrkjr
• https://mattermost.nethesis.it/nethesis/pl/8bfumprs3jgade68qf51popx7y

---

Thanks @lucagasparini for the suggestion! 🚀

[stephdl]

QA

target is ghcr.io/nethserver/mail:1.5.3-dev.1

the plugin is disabled by default, to enable it, add to environment file: DOVECOT_FLATCURVE_SUBSTRING_SEARCH=yes and restart dovecot container

use roundcubemail to make some search in your email

[lucagasparini]

The result obtained is not the desired one.

I recommend checking using this type of sender:
From: firstuser <firstuser@lg.nethserver.net> (not first.user)
In this case the search with the key user does not find anything with or without fts_flatcurve_substring_search.

If you disable the fts_flatcurve plugin completely:

~]# runagent -m mail1 podman exec -ti dovecot diff -u /etc/dovecot/local.conf.ori /etc/dovecot/local.conf
--- /etc/dovecot/local.conf.ori
+++ /etc/dovecot/local.conf
@@ -4,7 +4,7 @@

 login_trusted_networks = 10.5.4.0/24
 protocols = $protocols sieve
-mail_plugins = acl listescape notify mail_log fts fts_flatcurve quota
+mail_plugins = acl listescape notify mail_log fts quota
 mail_shared_explicit_inbox = yes

then

runagent -m mail1 podman exec -ti dovecot dovecot reload

the same search provides the expected result !