I have a group email set up.  It worked for a long time, then all of a sudden, it would send to only one of the four in the group.  I completely deleted the group and created a new one.  I did a test email and all in the group got it.  I then sent a real email and everyone got it.  I just sent another group email to the same group and only the first person listed in the group got it.  I can tell by the sent mail.