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Re: [ietf-smtp] Reject messages on backup mail exchangers when primary MX is online

2013-02-26 13:01:29
On 02/26/2013 06:31 PM, hector wrote:
Been developing and using greylisting for 9+ years in our package and everyone loves it. You have to make it work for your customers with advanced fast whitelisting ideas and with support for advanced "Smart" MTA ideas like SMTPGREY (http://tools.ietf.org/html/draft-santos-smtpgrey-02) its fits in better.
Sure there will be uses and when it helps to avoid spam, good!
I think the better approach is to "teach" the MTA how mail can be received and delivered more efficiently without wasted retries and delays. New SMTP extensions that attempt to inform clients about server/hosting attributes. That will probably mean a new DNS Server Policy discovery concept like the old Fidonet NODELIST which provided clients delivery times and whats was allowed to be transferred to servers. It even told clients when to use the BACKUP routing path guaranteed by FTSC policy to be always deliverable. The SMTPGREY proposal attempts to provide some reject intelligence to help the MTA reschedule its 2nd try. We have proof of concept that it indeed works in practice.
Yes, that sounds reasonable. Maybe it could even be combined with the XCLIENT proposal, so a retry will reach the same MX. (I understand that XCLIENT and SMTPGREY are really different beasts with different purposes.)
This is why its a complex queuing issue. Suppose I have 1000 messages for 1000 people at the same domain? How will you do the sending? Do all go to the first MX? Do you spread it? Are you shooting for fast throughput? What is the better queuing strategy? Does one fit all?
The answer is in the RFC I have quoted earlier for you. All 1000 messages MUST be tried by the client using the first MX. Hate it or love it, but that is what the RFC 5321 is for. And yes, I know, there is no way to check / enforce that, unfortunately I would say. Maybe the XCLIENT proposal can help in that regard.

Evert



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