[Dovecot] dovecot antispam plugin not found

[Alan Schmitt]

Hello,

I'm trying to setup dovecot-antispam, and even though the configuration
and the installation seem to have gone well, dovecot is telling me it's
not finding it.

Here is the symptom:

schmitta at top-wifi ~> /usr/local/Cellar/dovecot/2.2.10/libexec/dovecot/imap -c ~/.dovecotzimbra.rc
Fatal: Plugin 'antispam' not found from directory /usr/local/Cellar/dovecot/2.2.10/lib/dovecot

However there seems to be a plugin there:

schmitta at top-wifi ~> ls -al /usr/local/Cellar/dovecot/2.2.10/lib/dovecot/ | grep antispam
-rwxr-xr-x   1 schmitta  admin    38460 18 fév 22:40 lib90_antispam_plugin.bundle

I note that it is the only plugin with the ".bundle" extension, if it's
important.

My configuration file is as follows (I'm not finished with the antispam
configuration yet):

--8<---------------cut here---------------start------------->8---
protocols = imap
mail_location = maildir:~/.Maildir/zimbra:INBOX=~/.Maildir/zimbra/.INBOX

default_login_user = _dovenull
default_internal_user = _dovecot

protocol imap {
#  mail_plugins = $mail_plugins antispam
}

protocol lda {
  log_path = ~/.logs/dovecot-lda-errors.log
  info_log_path = ~/.logs/dovecot-lda.log
  mail_plugins = $mail_plugins sieve
}

plugin {
  sieve = ~/.dovecot.sieve
  sieve_plugins = sieve_extprograms
  sieve_extensions = +vnd.dovecot.filter
  sieve_filter_bin_dir = /usr/local/lib/dovecot/sieve-filter

  antispam_backend = DSPAM
  antispam_signature = X-DSPAM-Signature
}
--8<---------------cut here---------------end--------------->8---

Should I do something special to be able to load the antispam plugin?

Thanks,

Alan