header_str => [
        From => 'casey@geeknest.com',
        To => [ 'user1@host.com', 'Name <user2@host.com>' ],
        Cc => Email::Address::XS->new("Display Name \N{U+1F600}", 'user@example.com'),
    ],
...
    header_str => [
        From => 'my@address',
        To   => 'your@address',
    ],