John W. Baxter wrote: > On 1/31/07 1:38 AM, "Mike Cardwell" <[EMAIL PROTECTED]> wrote: > >> No one has mentioned why sender callouts without a null sender are "bad" >> yet. As far as I can see the worse that can happen is, a remote mail >> server connects to yours, and sends a "MAIL FROM" and a "RCPT TO". You >> then connect to the MX for the domain in the MAIL FROM, and do the same, >> using the value of the "RCPT TO" in the mail from of the callout. They >> then connect back to you to do a sender callout themselves. Then it >> stops due to the cache... And this would only happen in the rare >> circumstances that both servers are using sender callouts... > > Or you call out to a server that does greylisting 4xx responses at RCPT time > for most MAIL_FROM values, but at DATA time for <> (and the few obvious > other) MAIL_FROM values expecting that the calling-out server will never get > to DATA. So your callout is greylisted, and ... (what do you do?). (You > treat 4xx as success and all is well, or you treat it as callout failure, > then at best, they try again, your callout is accepted, and all is well > except that you have imposed a greylisting delay even though you don't do > greylisting.) > > I think. > > --John > > >
Correct. Observed in tests. But even other 'delays' can create timeout failures, so it is good to do <whatever> with traffic from '<>' to postmaster et al 'smartly', even if other traffic is handled at a more circumspect pace. Nor is it all *that* rare to have sender callouts at both ends. ISTR the sesame list server does 'em, (nicely cached, IRRC), so there should be evidence in most of our logs if/as/when we have imposed inordinate delays, greylisting on all traffic, etc. JM2CW Bill -- ## List details at http://www.exim.org/mailman/listinfo/exim-users ## Exim details at http://www.exim.org/ ## Please use the Wiki with this list - http://www.exim.org/eximwiki/
