After long time I discovery resolve the problem with spam, you know that Fortinet is not good (antiSpam) then you need configurate RBL list on your Fortigate. below has several list that block spam
edit 1
config entries
edit 1
set server " cbl.abuseat.org"
next
edit 2
set server " dnsbl.sorbs.net"
next
edit 3
set action reject
set server " bl.spamcop.net"
next
edit 4
set action reject
set server " xbl.spamhaus.org"
next
edit 5
set action reject
set server " dnsbl.spamhaus.org"
next
edit 6
set action reject
set server " sbl.spamhaus.org"
next
edit 7
set action reject
set server " opm.blitzed.org"
next
edit 8
set action reject
set server " dnsbl.njabl.org"
next
edit 9
set action reject
set server " zen.spamhaus.org" (This the Best List)
next
end
set name " Mylista_RBL"
next
end
You must see the link below, help you to configurate and put this server above.
http://kc.forticare.com/print.asp?id=377&Lang=1&SID=