Add rule for HELO host FQDN check

conf/lua/rspamd.lua

@@ -68,6 +68,24 @@ reconf['DATE_IN_PAST'] = function(task)
 	return false
 end
 
+reconf['HELO_NOT_FQDN'] = function(task)
+local helo = task:get_helo()
+
+local function check_regexp(str, regexp_text)
+    local re = regexp.get_cached(regexp_text)
+    if not re then re = regexp.create(regexp_text, 'i') end
+    if re:match(str) then return true end
+    return false
+end
+
+if helo then
+    if not check_regexp(helo, '(?=^.{4,255}$)(^((?!-)[a-zA-Z0-9-]{1,63}(?<!-)\\.)+[a-zA-Z]{2,63}$)') then
+        return true
+    end
+end
+
+return false
+end
 
 local function file_exists(filename)
 	local file = io.open(filename)