Multiple CNAMEs - howto?

[Hans]

> Incoming messages is not a problem - they *should* come to uk1
> primarily, and only to uk2 or 3 if the previous are unavailable.
>
> For that I have the setup:
>
> $ORIGIN mailnetwork.co.uk.
>    IN MX 10 uk1
>    IN MX 20 uk2
>    IN MX 30 uk3
>
> It's for outgoing messages so users can either connect to
> exchange.mailnetwork.co.uk (which will in effect be a round-robin for
> all 3 servers), or directly to uk1, 2 or 3.
> I believe mail clients use the A records for SMTP?

Not all depending on the definiton of  "mail clients".
For Postfix and Sendmail I am sure that the use MX before A on outbound 
mail.
But if we are talking over products like OE I can not say that.

I found this (old) discusion http://www.nber.org/redundant.html .
But I only can say check it.
So check your query logfile.
Even if you would have mutiple A records you should alway's see MX lookup 
request for that RR.