sending out broadcast emails ALL addresses are NOT sent – pick up of addresses appears to be random

Am new user to Window Live Mail.  I have set up several Group email accounts.  System recognizes number of addresses in account on register, HOWEVER, when invoking a group email, the system will only pick up about half of the addresses and the pick-ups appear to be random.   Very frustrating.   I am considering dumping Live Mail and using Thunderbird, unless you can fix this problem.   My email groups number anywhere from 20 to 50 persons.