Re: [exim] reverse_host_lookup and SERVFAIL

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Author: Ryan Tracey
Date:  
To: exim-users
Subject: Re: [exim] reverse_host_lookup and SERVFAIL
Hi Philip

>>temporary *local* problem."    I guess, though, that it might be difficult to
>>differentiate between their DNS being broken and the local DNS being broken.

>
>
> Quite. It is hard to generate short warning messages that cover every
> situation. It's a "local" problem in the sense that Exim can't get at
> the data it needs. It can't really tell where that data should come
> from.


That's what I thought. At any rate the other mail admin has been informed about his broken DNS and has agreed that it is a bad thing. Whether he fixes it is something else entirely.

>>Perhaps, if it's not there already, having some options for
>>reverse_host_lookup can be added to the wishlist: e.g.
>>reverse_host_lookup/ignore_servfail
>
>
> The problem is that you can't detect SERVFAIL at the level that Exim
> calls the resolver. The two deferring returns are TRY_AGAIN and
> NO_RECOVERY. In /usr/include/netdb.h, I see this:
>
> #define TRY_AGAIN       2       /* Non-Authoritative Host not found,
>                                    or SERVERFAIL.  */
> #define NO_RECOVERY     3       /* Non recoverable errors, FORMERR, REFUSED,
>                                    NOTIMP.  */

>
> TRY_AGAIN probably includes cases where the nameserver cannot be
> contacted.


Thanks for the explanation. Also, thanks for Exim: using it has made my job that much easier, challenging and enjoyable -- all at the same time.

Cheers,
Ryan