Re: [courier-users] 556 Address unavailable when mailing the backup mail server (also: dialback pythonfilter module)

[Marcus I. <mar...@gm...>]

Hi,

On Wed, Nov 12, 2008 at 9:37 PM, J. Pablo Fernández <pu...@pu...> wrote:
> Hello.
>
> I've configured a courier to receive email for another courier as a
> backup. When testing it I get the error:
>  556 Address unavailable.
> What does the error mean here?
>
> Does courier perform some kind of DNS check for the MX records (that is
> not set yet)?
> --
> J. Pablo Fernández <pu...@pu...> http://pupeno.com
>

incidentally I stumpled upon the same problem today, too. Check for
backscatter suppression, i.e. if there was another error before this
one.

In my case I found that the dialback module in pythonfilter was having
problems with receiving mails being relayed from my backup MX.
Had to disable it for now. In case anybody has seen this message
before, it was: 400 SMTP class exception during connect

I took a cursory glance at the source code I found that it splits the
source address into user and domain and then tries to connect to the
MX of the resulting domain.
Quite straightforward, really. Yet, in my case, it looks like every
mail coming in from my backup MX produced the aforementioned error
message while every mail being received directly came through without
problems.
Row 250 in dialback.py was the only place where I found this error
message referenced. Any hints?
And I better mention that sending mail from this server and IP works
fine, too, so it's not the firewall blocking outgoing SMTP.

Best regards
Marcus