# multipart message
my @parts = (
    Email::MIME->create(
        attributes => {
            ...                    
        },
        body => io( ... )->all,
    ),
    Email::MIME->create(
        attributes => {
            ...                    
        },
        body => io( ... )->all,
    ),
);

my $email = Email::MIME->create(
    header => [ ... ],
    parts  => [ @parts ],
);