my $string = "Rückantwort";

my @parts = split /\n\n/,$string;
for my $part ( @parts ){
    next unless $part =~ m!^\s*Volume!;
    print $part;
}

my $file = '/path/to/file';

{
    local $/ = "\n\n";
    open my $fh,'<',$file or die $!;
    while( my $entry = <$fh> ){
        next unless $entry =~ m!^\s*Volume!;
        print $entry;
    }
}