doveconf syntax question

[A. Schulze]

Am 05.01.2016 um 15:31 schrieb A. Schulze:
> I have one sieve extension enabled:
>
>    /etc/dovecot/conf.d/20-sieve.conf:
>
>    plugin {
>      sieve_extensions = +vacation-seconds
>    }
>
> now (months later) we want to enable an other extension.
> no big deal:
>
>    /etc/dovecot/local.conf:
>
>    plugin {
>      sieve_extensions = +editheaders
>      ...
>    }
>
> This was wrong. We ASSUMED the plus would add the extension to the list.
> But at the end only +editheaders was activ.
>
> What's the right way to /add/ sieve_extensions from different config files?
> our guess "sieve_extensions = $sieve_extensions +editheaders" do not work:
>
> doveconf -a | grep sieve_extensions
> doveconf: Fatal: Error in configuration file /etc/dovecot/local.conf line 22: Unknown variable: $sieve_extensions
> doveconf: Error: managesieve-login: dump-capability process returned 89
> doveconf: Fatal: Error in configuration file /etc/dovecot/local.conf line 22: Unknown variable: $sieve_extensions

no opinions so far?