[Mimedefang] Re: Filtering idea for stock pump&dumps

[Jeff Rife]

On 3 Jul 2007 at 11:24, Kevin A. McGrail wrote:

> "It is difficult to assign a meaning to "transient" when two different sites 
> (receiver- and sender-SMTP agents) must agree on the interpretation.  Each 
> reply in this category might have a different time value, but the SMTP 
> client is encouraged to try again.  "
> 
> In RFC-speak, the word encouraged is not MUST.  Greylisting in and of itself 
> may put your email at risk because there is no requirement that mail be 
> retried per the RFC except based on existing implementation.
> 
> In short, for Microsoft not to try again is not against the RFC for a 4yz 
> error code it seems if I read the result codes section of 2821 correctly.

Yes, it's not against RFC, but Exchange *does* retry 4yz responses, 
just not if they come at the "RCPT TO" phase.

Since I can think of at least a few perfectly legitimate reasons to 
tempfail at RCPT (over quota, can't contact internal server to verify 
the user exists, etc.), the fact that they don't do this really is 
stupid, and the more people who cater to it just makes them not care 
about fixing it.  In addition, I believe it is possible to configure 
Exchange itself to respond with a 4xy in response to certain "RCPT TO" 
problems, so basically it's an MTA that can't even talk to itself.

As I said before, because of all the known bugs (both sending and 
receiving), anybody who lets Exchange talk directly to the Internet is 
just asking for trouble, and any sane admin has a setup where that 
doesn't happen.


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Jeff Rife |  
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