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

---

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 !

[DavidePrincipi]

I tested in a production server and it seems to return the correct results.

• Update to 1.5.3-dev.1
• Set DOVECOT_FLATCURVE_SUBSTRING_SEARCH=yes in environment
• Reload with systemctl --user reload dovecot

Searches in From now match by substring.

• Set DOVECOT_FLATCURVE_SUBSTRING_SEARCH=no in environment
• Reload with systemctl --user reload dovecot

Searches in From do not match by substring.

Note: After reload it may take a while to become effective if there is an open IMAP session. Within Webtop I did a logout/login.

VERIFIED

[DavidePrincipi]

Flatcurve substring search works for new installations, however on upgraded installations the indexes must be rebuilt.

The resulting index require much more disk space, because each substring needs to be indexed.

Please provide an alternative to Flatcurve substring search: let's add an environment variable that can disable FTS+Flatcurve plugin completely, to rely on the vanilla RFC-compliant search of Dovecot.

[stephdl]

QA

test with the mail:1.5.3-dev.2

• verify the flatcurve is still enabled in configuration and verify the dovecot container is still working as expected
• then disable fts flatcurve and verify the dovecot container is still working as expected

[lucagasparini]

VERIFIED

Tested with both new installation and update