On Wed, 2007-12-05 at 13:57 -0800, Marc Perkel wrote:
> Having a small issue.
>
> set acl_c_rdns = ${lookup dnsdb{ptr=$sender_host_address}{$value}{}}
>
> Works except that if the lookup fails I get DEFER. What I want is if the
> lookup fails to get an empty string. What am I doing wrong?
Well...
http://www.exim.org/exim-html-current/doc/html/spec_html/ch09.html#SECTdnsdb
states:
"If the lookup does not succeed, the fail keyword causes a forced
expansion failure – see section 11.4 for an explanation of what this
means."
...and in turn,
http://www.exim.org/exim-html-current/doc/html/spec_html/ch11.html#SECTforexpfai states:
"If, instead of a “false” substring, the word “fail” is used (not in
braces), the entire string expansion fails in a way that can be detected
by the code that requested the expansion."
This is handled differently according to the expansion in use. In your
case, it's a dnsdb lookup, so the following applies:
http://www.exim.org/exim-html-current/doc/html/spec_html/ch09.html#SECID67
"The dnsdb lookup fails only if all the DNS lookups fail. If there is a
temporary DNS error for any of them, the behaviour is controlled by an
optional keyword followed by a comma that may appear before the record
type. The possible keywords are “defer_strict”, “defer_never”, and
“defer_lax”. With “strict” behaviour, any temporary DNS error causes the
whole lookup to defer. With “never” behaviour, a temporary DNS error is
ignored, and the behaviour is as if the DNS lookup failed to find
anything. With “lax” behaviour, all the queries are attempted, but a
temporary DNS error causes the whole lookup to defer only if none of the
other lookups succeed."
I believe the answer lies therein :)
Graeme
