A little more testing after not getting an invite on an account that is a member of FB.
3 accounts, 2 are members of FB, both Hotmail, one is not, my domain.
No invites received.
OK, since the one I did receive was the top email, maybe that has something to do with it, move them around, put an hotmail address that is a member on top, surely I will get an invite.
No invites received for all three.
Ok, test three, bring back the hotmail non member, put it third on the list, last time it was first, 1 hotmail member, 1 my domain, different one that I know is not block, the other was not either, but double checking, non member. lets see what happens.
Hotmail member, no invite
My domain non member, no invite
Hotmail non member, invite. So, it has now got two invites. I checked it first, within a minute.