You could maybe use the following to break out the individual items in the list field but am having trouble imagining what the rest of your stats command output is - haven't had enough caffeine yet I suppose.
| makemv list | mvexpand list
At any rate you would then need another stats (+ sort & head) or top command to then get your top X.
$SEARCH | stats count dc(mymail) as unique count(mymail) as hits values(mymail) as list by VAR
| eval sno=mvrange(0,10,1) | eval list=mvzip(list,sno,",") |nomv list| eval list=replace(list,"(,\d+)"," ") | makemv list
The no '10' in the mvrange command denotes you will be returned first 10 values from the multivalued field 'list'