Dovecot 2.4 - Issue with plugin at 90-sieve.conf

[Andreas Günther]

Hello,
it's me again, with another undocumented upgrade problem with Dovecot.

My 90-sieve.conf file used in Dovecot 2.3.19.1 looked like this:
plugin {
  sieve = file:~/sieve;active=~/.dovecot.sieve
  recipient_delimiter = +
  acl = vfile
  acl_anyone = allow
  acl_shared_dict = file:/var/vmail/shared-mailboxes.db
  quota = dict:Userquota::proxy::default
  quota_rule2 = Trash:storage=+100%%
  sieve = /var/vmail/%d/%n/sieve/active-script.sieve
  sieve_before = /var/vmail/sieve/global.sieve
  sieve_dir = /var/vmail/%d/%n/sieve/scripts/
  sieve_max_script_size = 1M
  sieve_quota_max_scripts = 0
  sieve_quota_max_storage = 0
}

If I adopt this in Dovecot 2.4.1, I will get...
doveconf -n
doveconf: Fatal: Error in configuration file /etc/dovecot/conf.d/90-sieve.conf 
line 118: Unknown section name: plugin

This is exactly the plugin{..} section in 90-sieve.conf.

The document at https://doc.dovecot.org/2.4.0/installation/upgrade/2.3-to-2.4.html#removed-features mentions:
"plugin - All plugin settings are now global settings."

An AI search revealed that plugins should now be located in the service 
section. So,
I set exactly this in the "service imap" section of the 10-master.conf file:

service imap {
  vsz_limit = 1G
  process_limit = 1024

  # Plugin section for Sieve
  plugin {
    sieve = file:~/sieve;active=~/.dovecot.sieve
    recipient_delimiter = +
    acl = vfile
    acl_anyone = allow
    acl_shared_dict = file:/var/vmail/shared-mailboxes.db
    quota = dict:Userquota::proxy::default
    quota_rule2 = Trash:storage=+100%%

    # Sieve specific settings
    sieve_before = /var/vmail/sieve/global.sieve
    sieve_dir = /var/vmail/%d/%n/sieve/scripts/
    sieve_max_script_size = 1M
    sieve_quota_script_count = 0
    sieve_quota_storage_size = 0
  }
}

The result remains the same:
doveconf -n
# 2.4.1-4 (7d8c0e5759): /etc/dovecot/dovecot.conf
# Pigeonhole version 2.4.1-4 (0a86619f)
doveconf: Fatal: Error in configuration file /etc/dovecot/conf.d/10-master.conf 
line 74: Unknown section name: plugin

Now I really don't know anymore how anything is supposed to be configured. 
Above all, these parts are definitely poorly documented.
I also hope for further valuable information that will solve the problem.

Greetings

Andreas