Author: Russell King Date: To: Dermot Paikkos CC: Exim-users Subject: Re: [exim] sender verify callout to non smtp source
On Wed, Mar 09, 2005 at 11:14:16AM -0000, Dermot Paikkos wrote: > > It does a callout verification against the MX servers for the domain
> > of the envelope sender.
>
> I thought that it would query the sending host as it would already
> have the ip address for that host so it would presumabley be quickier
> to respond directly to them rather than to a dnslookup. Also from the
> section on callout verification:
>
> "One way this can be done is to make an SMTP callback to the sending
> host (for a sender address)"
The reason this isn't done is because the sending host may not be the
host which accepts mail for that envelope sender address. Consider a
large ISP, where there are two sets of mail servers. One set are for
outgoing mail only, which do not listen for SMTP on the public internet.
The other set is for incoming mail only, which do.
Therefore, trying to contact the sending host will always fail.
> Which seemed to imply that it would call back the incoming host.
>
> In this case the return-path was
> Return-path: <nobody@???>
> but the sender was
> From: kevin.davis@???
>
> i imagine this isn't considered good practise.
You are correct.
> > It sounds like you need to tweak your plugin configuration to set
> > the sender address appropriately.
>
> yes we need to do that.
