[courier-users] Re: Fallback to backup (secondary) MX

[Martin H. <ho...@ma...>]

Yes, I agree that problem is in proxy, which shouldn't act like that. 
But I must use it, and I cannot use direct outbound SMTP, because our 
proxy is virus detector.
When I reported problem at our proxy vendor, I was told (by smart people 
in Symantec), that sendmail has no problem with that, and that it tries 
backuf MX after receiving error 421.
So it seems, that I will have to test another mailer :-( I hope, that 
postfix will work, because I don't want to use dinosaur sendmail.

Thank you for your help,
Martin Horak

> From: Martin Horak [mailto:[EMAIL PROTECTED]
>  >
>  > > > Hello courier users.  I have a problem with courier server -
>  > > > especially SMTP module.  I send a mail through transparent mail
>  > > > proxy on our firewall. When the primary MX of recipient's domain
>  > > > in unreachable, i get this reply from relay:
>  > > > 421 4.4.1 Unable to contact destination
>  > >
>  > > There is no such error message in Courier.
>  >
>  > Of course, this message comes from our damned firewall/mail proxy,
>  > when remote MTA is unreachable.
>  >
>  > > > Other MX records aren't tried and the mail is deferred. I'd like
>  > > > courier to contact backup MX'es before deferring the mail.  How
>  > > > can I achieve this?
>  > >
>  > > You can achieve what you want by learning a little bit about SMTP
>  > > first.  If the above message is received in response to a delivery
>  > > attempt, the message is interpreted as an indication of a
>  > > temporary failure, and to try again later.  That is "later", and
>  > > not "try another mail relay now".  Do to otherwise would be a
>  > > behavior more akin of a spam generator, and is likely to get you
>  > > blacklisted as such
>  >
>  > OK, do I have any chance to change Courier's response to this
>  > errorcode (421) from 'try again later' to 'try another relay'?  I
>  > really don't want to switch to another mailserver - I'm used to
>  > Courier and i think it has better concept than any other MTA.  But
>  > this feature/bug is quite critical for me.
> 
> I'm not sure any mailserver will act the way you want.  The errorcode
> 4xx indicates to Courier that it has reached the destination
> mailserver and has been told to try again later.  Since Courier thinks
> that it has received a response from the primary MX server, it has no
> reason to attempt the secondary.
> 
> It looks like your problem is with the proxy.  The proxy is acting
> like an MTA and giving bogus error codes.  In other words, it's not
> quite as transparent as you think.
> 
> If you allow Courier to use direct outbound SMTP rather than going
> through the proxy, things would work the way you expect.
> 
>  > One more question: In what circumstances Courier falls back to
>  > backup (secondary) MX?
> 
> Courier will fall back to the secondary if it does not receive a
> response from the primary.
> 
> Bowie