This component implements a greylisting SMTP proxy protocol, by subclassing ConcreteMailHandler and overriding the appropriate methods (primarily the shouldWeAcceptMail method).
For more detail, please see http://www.kamaelia.org/KamaeliaGrey
You use this as follows (at minimum):
ServerCore(protocol=GreyListingPolicy, port=25)
If you want to have a hardcoded/configured greylisting server you could do this:
class GreyLister(ServerCore): class protocol(GreyListingPolicy): allowed_senders = [] allowed_sender_nets = [] allowed_domains = [ ] GreyLister(port=25)
Primarily it override the method shouldWeAcceptMail, and implements the following logic:
if self.sentFromAllowedIPAddress(): return True # Allowed hosts can always send to anywhere through us if self.sentFromAllowedNetwork(): return True # People on truste networks can always do the same if self.sentToADomainWeForwardFor(): try: for recipient in self.recipients: if self.whiteListed(recipient): return True if not self.isGreylisted(recipient): return False except Exception, e: pass return True # Anyone can always send to hosts we own
Clearly AllowedIPAddress, AllowedNetwork, whiteListed, and DomainWeForwardFor are fairly clear concepts, so for more details on those please look at the implementation.
isGreylisted by comparison is slightly more complex. Fundamentally this works on the basis of saying this:
- have we seen the triple (ip, sender, recipient) before ?
- if we have, then allow the message through
- otherwise, defer the message
Now there is a little more subtlty here, based on the following conditions:
- If greylisted, and not been there too long, allow through
- If grey too long, refuse (restarting the greylisting for that combo)
- If not seen this triplet before, defer and note triplet
- If triplet retrying waaay too soon, reset their timer & defer
- If triplet retrying too soon generally speaking just defer
- If triplet hasn't been seen in aaaages, defer
- Otherwise, allow through & greylist them
Got a problem with the documentation? Something unclear that could be clearer? Want to help improve it? Constructive criticism is very welcome - especially if you can suggest a better rewording!
Please leave you feedback here in reply to the documentation thread in the Kamaelia blog.
-- Automatic documentation generator, 19 Oct 2008 at 14:29:09 UTC/GMT