Ok, first of backup files you edit.
You should make /etc/postfix/main.cf
mydestination = localhost, localhost.$mydomain
look like this or a variation of this, becouse you allready made destination hosts with ispconfig witch are writen in your sql database so postconfig reads sql and this and there should not be 2 times the entry, so try going with suggestion i made you.
after that requing all messages in console:
postsuper -r ALL
see what heapens, this should solve your reciving mail problem
EonTek.rs - System Engineering