...

$enable_dkim_signing = 0;    # load DKIM signing code, keys defined by dkim_key
dkim_key('nausch.org', '140228', '/var/amavis/dkim/dkim-key-140228.pem
', h=>'sha256'); # Nausch.org's Mailserver DKIM-Schluessel
@dkim_signature_options_bysender_maps = (
    { '.' => { ttl => 21*24*3600, c => 'relaxed/simple' } } # catchall defaults
                                        ); 

...