Milter-greylist

Hi to all,

milter-greylist README file says resolver must be thread-safe in order 
to be able to use dnsrbl feature.


So, to verify that, I typed "nm milter-greylist|grep res" and it says :
---------------------------------------------------------
U __res_nclose@@GLIBC_2.2
U __res_ninit@@GLIBC_2.2
U __res_nquery@@GLIBC_2.2
---------------------------------------------------------
instead of res_init or nres_init like written in README file

Can I say my resolver is thread-safe ?