On 2012-05-23 at 12:36 -0400, Phil Pennock wrote:
> The dnslookup router will decline if the domain does not exist in DNS,
> or the domain is not syntactically valid for SMTP's defined DNS lookups,
> or the MX record points to ".", which is a convention for "no MX service
> for this domain, and do not fall back to A/AAAA lookups". There's a
> couple of other cases too.
I've added a new section to the documentation for dnslookup; this will
be in the 4.80 release's docs, and on the website when 4.80 goes out.
Regid, thanks for drawing my attention to how this could be better
documented.
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17.2 Declining addresses by dnslookup
-------------------------------------
There are a few cases where a dnslookup router will decline to accept an
address; if such a router is expected to handle "all remaining non-local
domains", then it is important to set no_more.
Reasons for a dnslookup router to decline currently include:
* The domain does not exist in DNS
* The domain exists but the MX record's host part is just "."; this is a
common convention (borrowed from SRV) used to indicate that there is no
such service for this domain and to not fall back to trying A/AAAA records.
* Ditto, but for SRV records, when check_srv is set on this router.
* MX record points to a non-existent host.
* MX record points to an IP address and the main section option
allow_mx_to_ip is not set.
* MX records exist and point to valid hosts, but all hosts resolve only to
addresses blocked by the ignore_target_hosts generic option on this router.
* The domain is not syntactically valid (see also allow_utf8_domains and
dns_check_names_pattern for handling one variant of this)
* check_secondary_mx is set on this router but the local host can not be
found in the MX records (see below)
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Regards,
-Phil
