On Mon, 2008-12-22 at 17:04 -0800, Gordon Messmer wrote: > I believe it could be configured to > report success or failure to the sender in the event that at least one > recipient refused the message. It's been a while since I used it, so I > don't remember clearly. A courier filter could do the same thing, but > the implementation would be somewhat longer than the one I've included.
This is the logical issue that Sam addresses in Courier with the enigmatic "412 You are not whitelisted ...." message and others like it. The SMTP protocol wasn't designed to deal with message acceptance or rejection based on per-recipient analysis of the DATA section of a message. Say an email is address to users X, Y and Z on a system, and let's say that user X has tighter content filtering criteria than user Y or Z. The sending SMTP client sends 3 RCTP TO exchanges, and the server must accept all 3, knowing only that all 3 are legitimate addresses on the system. The client has received the "250 Ok." responses and they're a done deal. Then comes the DATA segment and suppose the message passes for users Y and Z but not for user X. The receiving server has no way, within the context of the SMTP protocol, to inform the sending client at this point that 1 of the 3 recipients has rejected the message while it was OK for the other 2. It must, at this point, either reject the message for all 3, or accept for all 3, and this is generally considered unacceptable. Sam deals with this by having Courier preemptively back out on the receiving end if it finds that content analysis is enabled for the exchange between the sender and one of the recipients and not for the sender and another of the recipients. In this case, Courier never makes it to the DATA exchange and the SMTP session is aborted for all recipients. This isn't possible, however, when content analysis is enabled for _all_ recipients, but the per-recipient verdict on acceptance or rejection isn't rendered until after the DATA portion of the message has been sent. It's a basic logical flaw in the SMTP protocol. Originally, the DATA segment of an email was considered sacred and SMTP clients and server weren't to touch it, except to add their own headers as it passed through. These days, what with spam, viruses, Microsoft, etc., it's a lot more dicey. -- Lindsay Haisley | "Everything works | Accredited FMP Computer Services | if you let it" | by the 512-259-1190 | (The Roadie) | Austin Better http://www.fmp.com | | Business Bureau ------------------------------------------------------------------------------ _______________________________________________ courier-users mailing list [email protected] Unsubscribe: https://lists.sourceforge.net/lists/listinfo/courier-users
