Thomas Klaver wrote:

> Is it possible to retrieve the highest prioritized MX record using a
> dnsdb lookup? If so, how?

The results returned by dnsdb when doing an mx or mxh lookup are not 
ordered by priority:

r...@haven:~# exim4 -be '${lookup dnsdb{mx=googlemail.com}}'
30 alt3.gmail-smtp-in.l.google.com
40 alt4.gmail-smtp-in.l.google.com
5 gmail-smtp-in.l.google.com
10 alt1.gmail-smtp-in.l.google.com
20 alt2.gmail-smtp-in.l.google.com
r...@haven:~#

I'm not sure how you could pick out the item with the lowest priority 
using Exim expansions.

> How would dnsdb affect a server's load? We're talking about a fallback
> platform for approximately 500+ domains - and growing.

It's extremely light weight compared to everything else that will be 
going on inside Exim. I doubt it would affect the server load noticably.

> Are results of a dnsdb lookup cached? If that may be the case, for how
> long are they cached?

Nope. Use a caching dns server.

-- 
Mike Cardwell
(https://secure.grepular.com/) (http://perlcv.com/)

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