To start:

1) compile checker by running "make"
2) run "./script.sh" (with options you've described in the task description)

  $ time ./script.sh 
  Parsing CIDRs... ok
  Starting checker daemon...ok
  Processing emails now
  
  real	0m19,689s
  user	0m11,364s
  sys	0m4,084s
  
  $ LANG=C wc -l email.txt.*
    104 email.txt.match
    349 email.txt.nomx
    547 email.txt.unmatch
   1000 total

Notes:
Checker was a speed-hack, because I said I finish this work in 24
hours. Some stuff is hardcoded. F.e. it uses "/tmp/checker.socket" and
it's not configurable.

Don't worry about 19s of real time. 14s is CIDR parsing:
  Parsing CIDRs... 
  real	0m13,923s
  user	0m1,084s
  sys	0m1,540s

Now it's your time to play with configuration options and workers number.
Btw I've added more options. Just look at the beginning of the script. It must be obvious.

Dependencies:
These tools must be available in your system: bash getopt socat bc dig tr