DKIM signing for the multiple domain

[kshitij mali]

I have 5 domain through which the out bound email sre getting deilverd how
to sign all 5 of these .

the below syntax/example explains only the single domain configuration how
to get signed for the multiple domain what change i need to the below config
of amavisd.conf

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 $enable_dkim_verification = 1;
  $enable_dkim_signing = 1;
  dkim_key('example.com', 'foo', '/var/db/dkim/example-foo.key.pem');

  @dkim_signature_options_bysender_maps = (
    { '.' => { ttl => 21*24*3600, c => 'relaxed/simple' } } );
  @mynetworks = qw(0.0.0.0/8 127.0.0.0/8 10.0.0.0/8 172.16.0.0/12

                   192.168.0.0/16);  # list your internal networks

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Regards,
Kshitij