Controlling awk array output

I have some log files containing FQDNs that I need to aggregate at the third level (three.two.tld); to do that I split it, reverse print the desired number of levels:

   awk '{print$2}' consolidated.txt|awk -F. '{for(i=NF;i>NF-3;i--){printf ".%s",$i};printf "\t%s\n",$0}'

Leading "." aside, that does what I need where NF>2, e.g.

   .com.microsoft.mp       fee3.delivery.mp.microsoft.com

However, microsoft.com becomes:

   .com.microsoft.com.microsoft      microsoft.com

          

Try as I might, I cannot get my head around how to handle second-level-only domains (example.com) whilst still aggregating the remainder at three. I've tried adding if statements to the array output, but with no success.

Can someone please point me in the right direction?