ACZoom

blockhosts cannot work with fully qualified names - it needs IP addresses.

Looking at the pure-ftpd documention, it shows this:

-H  --dontresolve  
'-H': By default, fully-qualified host names are logged. To achieve this,
DNS lookups are mandatory. The '-H' flag avoids host names resolution.

So, unless you can run pure-ftpd with the -H or --dontresolve option, blockhosts cannot do its work.