Dovecot 2.3 in NixOS 26.05

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1

I am trying to upgrade a machine running dovecot and managesieve from NixOS 25.11 to 26.05.

I run into the following issue: dovecot 2.3 cannot start because it is looking for 2.4 plugins. This is visible in journalctl but also when running doveconf:

[root@server:~]# doveconf

# 2.3.21.1 (d492236fa0): /etc/dovecot/dovecot.conf

doveconf: Error: Couldn’t load plugin /run/current-system/sw/lib/dovecot/modules/settings/libmanagesieve_login_settings.so: dlopen() failed: /nix/store/9m0p75xkd2kmawzj61xngzl5rmczfnnj-dovecot-2.4.4/lib/dovecot/libdovecot-storage.so.0: undefined symbol: unicode_code_points_index16
doveconf: Error: Couldn’t load plugin /run/current-system/sw/lib/dovecot/modules/settings/libmanagesieve_settings.so: dlopen() failed: /run/current-system/sw/lib/dovecot/modules/settings/libmanagesieve_settings.so: undefined symbol: settings_boollist_get
doveconf: Error: Couldn’t load plugin /run/current-system/sw/lib/dovecot/modules/settings/libpigeonhole_settings.so: dlopen() failed: /nix/store/9m0p75xkd2kmawzj61xngzl5rmczfnnj-dovecot-2.4.4/lib/dovecot/libdovecot-storage.so.0: undefined symbol: unicode_code_points_index16

I don’t want to Dovecot 2.4 now (my system.StateVersion is 24.05) so Dovecot 2.3 should be used. It seems there is a mixup between 2.3 and 2.4 when generating the config. But I could not find bug reports about this in GitHub. Am I really the only one who encounters this? How to proceed? (or better: how to make it work?).

from my config:

services.dovecot2 = {
  enable = true;

  enablePAM = false;
  settings = {

    protocols = [
      "submission"
      "sieve"
      "imap"
      "lmtp"
    ];

    ssl_cert = sslCert;
    ssl_key = sslKey;
    mail_location = "mdbox:${mailLocation}/%u";

    submission_relay_host = "localhost";
    submission_relay_trusted = true;

    auth_username_format = "%Ln";
    recipient_delimiter = ".";

    "service lmtp" = {
      "unix_listener dovecot-lmtp" = {
        group = config.services.postfix.group;
        mode = "0600";
        user = config.services.postfix.user;
      };
    };

    userdb = {
      driver = "ldap";
      args = ldapUserDbConfig;
    };

    passdb = {
      driver = "ldap";
      args = ldapPassDbConfig;
    };

    plugin = {
      sieve = "file:\~/sieve;active=\~/.dovecot.sieve";
      sieve_extensions = [ "+fileinto" ];

    };
  };

  mailPlugins.perProtocol.lmtp.enable = [ "sieve" ];

};

environment.systemPackages = [ pkgs.dovecot_pigeonhole ];

hmm, it looks like there is no version of dovecot_pigeonhole for dovecot 2.3

2

environment.systemPackages = [ pkgs.dovecot_pigeonhole_0_5 ];

Funny, it took me a month to figure this out, and when I create a help post on this forum I solve it within minutes

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